A muon spin rotation (μSR) experiment was conducted to investigate the magnetic ground state of single-crystalline RuO₂. The study found no evidence of a spontaneous internal magnetic field (B_loc) expected in a magnetically ordered phase over the temperature range 5–400 K. First-principles calculations suggested that the Ru magnetic moment (|m_Ru|) is much smaller than previously reported, with an upper limit of 4.8(2) × 10⁻⁴ μB. These results indicate that the antiferromagnetic (AFM) order, as reported, is unlikely to exist in the bulk crystal. RuO₂, with a rutile structure, is a material with high catalytic activity and chemical stability. It has been considered an ordinary Pauli paramagnetic metal, but recent studies suggest it has a topological electronic structure and may exhibit AFM order with a high Néel temperature (>300 K) and a Ru magnetic moment of ~0.05 μB. The presence of AFM order has generated interest in its potential applications for spintronic devices and strain-induced superconductivity. Theoretical predictions and experimental results for various anomalies related to transport phenomena have been reported, including the anomalous Hall effect and spin current due to the spin-splitter effect. However, the reported size of Ru magnetic moments is close to the sensitivity limit of neutron and X-ray diffraction experiments. A recent theoretical study suggests that AFM ordering may be induced by hole doping due to Ru vacancies in RuO₂, which is intrinsically nonmagnetic. Therefore, verification of the AFM phase with local magnetic probes is required. The μSR experiment showed that the spontaneous muon spin precession signal expected in a magnetically ordered phase was not observed. The first-principles density functional theory (DFT) calculations of muon sites excluded the possibility that muons are localized at sites where the internal magnetic field cancels out. These results support the scenario that the bulk crystal RuO₂ is a nonmagnetic metal. μSR is a sensitive probe for internal magnetic fields, with applications in studying AFM ordering in high-Tc cuprate superconductors and superconductivity. The muon implantation energy is high enough to be surface-independent and bulk-sensitive, and the implanted muons decay with an average lifetime of 2.2 μs, making them suitable for μSR measurements. The study used DFT calculations to investigate the muon stopping sites in RuO₂, finding that the most stable site for hydrogen (Site1) is about 0.1 nm from the nearest oxygen. The total energy calculations showed that the total energies at the 8j and 4d sites are higher than Site1, ruling out the possibility that muons are stationary at these sites where B_loc cancels out. The study also calculated the local magnetic field (BA muon spin rotation (μSR) experiment was conducted to investigate the magnetic ground state of single-crystalline RuO₂. The study found no evidence of a spontaneous internal magnetic field (B_loc) expected in a magnetically ordered phase over the temperature range 5–400 K. First-principles calculations suggested that the Ru magnetic moment (|m_Ru|) is much smaller than previously reported, with an upper limit of 4.8(2) × 10⁻⁴ μB. These results indicate that the antiferromagnetic (AFM) order, as reported, is unlikely to exist in the bulk crystal. RuO₂, with a rutile structure, is a material with high catalytic activity and chemical stability. It has been considered an ordinary Pauli paramagnetic metal, but recent studies suggest it has a topological electronic structure and may exhibit AFM order with a high Néel temperature (>300 K) and a Ru magnetic moment of ~0.05 μB. The presence of AFM order has generated interest in its potential applications for spintronic devices and strain-induced superconductivity. Theoretical predictions and experimental results for various anomalies related to transport phenomena have been reported, including the anomalous Hall effect and spin current due to the spin-splitter effect. However, the reported size of Ru magnetic moments is close to the sensitivity limit of neutron and X-ray diffraction experiments. A recent theoretical study suggests that AFM ordering may be induced by hole doping due to Ru vacancies in RuO₂, which is intrinsically nonmagnetic. Therefore, verification of the AFM phase with local magnetic probes is required. The μSR experiment showed that the spontaneous muon spin precession signal expected in a magnetically ordered phase was not observed. The first-principles density functional theory (DFT) calculations of muon sites excluded the possibility that muons are localized at sites where the internal magnetic field cancels out. These results support the scenario that the bulk crystal RuO₂ is a nonmagnetic metal. μSR is a sensitive probe for internal magnetic fields, with applications in studying AFM ordering in high-Tc cuprate superconductors and superconductivity. The muon implantation energy is high enough to be surface-independent and bulk-sensitive, and the implanted muons decay with an average lifetime of 2.2 μs, making them suitable for μSR measurements. The study used DFT calculations to investigate the muon stopping sites in RuO₂, finding that the most stable site for hydrogen (Site1) is about 0.1 nm from the nearest oxygen. The total energy calculations showed that the total energies at the 8j and 4d sites are higher than Site1, ruling out the possibility that muons are stationary at these sites where B_loc cancels out. The study also calculated the local magnetic field (B