This study reports on the ultrahigh mobility and giant magnetoresistance (MR) observed in the Dirac semimetal Cd3As2. The material exhibits an exceptionally high carrier mobility of 9×10^6 cm²/Vs at 5 K, attributed to a strong protection mechanism against backscattering. This protection leads to a transport lifetime 10^4 times longer than the quantum lifetime. When a magnetic field is applied, this protection is lifted, resulting in a large MR. The MR is found to be highly sensitive to the magnetic field, with the MR profile changing from H-linear to H^α (α=2-2.5) as mobility increases. The study also reveals that the Fermi surface is nearly isotropic, with a high Fermi velocity of 9.3×10^5 m/s and a Fermi energy of 232 mV. The SdH oscillations are well described by the Lifshitz-Kosevich expression, indicating a single Fermi surface. The results suggest that the high mobility in Cd3As2 is due to a unique protection mechanism against backscattering, which is not observed in other materials like GaAs/AlGaAs 2DEG. The study also excludes the presence of a second band in Cd3As2, as no additional SdH peaks are observed. The findings highlight the unique electronic properties of Cd3As2, which could have implications for future electronic devices.This study reports on the ultrahigh mobility and giant magnetoresistance (MR) observed in the Dirac semimetal Cd3As2. The material exhibits an exceptionally high carrier mobility of 9×10^6 cm²/Vs at 5 K, attributed to a strong protection mechanism against backscattering. This protection leads to a transport lifetime 10^4 times longer than the quantum lifetime. When a magnetic field is applied, this protection is lifted, resulting in a large MR. The MR is found to be highly sensitive to the magnetic field, with the MR profile changing from H-linear to H^α (α=2-2.5) as mobility increases. The study also reveals that the Fermi surface is nearly isotropic, with a high Fermi velocity of 9.3×10^5 m/s and a Fermi energy of 232 mV. The SdH oscillations are well described by the Lifshitz-Kosevich expression, indicating a single Fermi surface. The results suggest that the high mobility in Cd3As2 is due to a unique protection mechanism against backscattering, which is not observed in other materials like GaAs/AlGaAs 2DEG. The study also excludes the presence of a second band in Cd3As2, as no additional SdH peaks are observed. The findings highlight the unique electronic properties of Cd3As2, which could have implications for future electronic devices.