This paper presents a novel mini-resonant photoacoustic sensor designed for high-sensitivity trace gas sensing. The sensor consists of a sphere-cylinder coupled acoustic resonator, a cylindrical buffer chamber, and a fiber-optic acoustic sensor. The first-order resonance frequency of the mini-resonant photoacoustic sensor is significantly reduced compared to conventional T-type resonant photoacoustic sensors, achieving a volume of only 0.8 cm³. The sensor was tested using trace methane as the target gas, achieving a detection limit of 101 parts-per-billion at a 100-second integration time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 1.04 × 10⁻⁸ W·cm⁻¹·Hz⁻¹/². The sensor's performance is superior to previously reported resonant and non-resonant PAS sensors, making it suitable for high-sensitivity miniaturized trace gas sensing in confined spaces. The study also includes detailed simulations and experimental results to validate the sensor's performance, demonstrating its potential for practical applications in various fields such as medical diagnosis, combustion diagnostics, and environmental monitoring.This paper presents a novel mini-resonant photoacoustic sensor designed for high-sensitivity trace gas sensing. The sensor consists of a sphere-cylinder coupled acoustic resonator, a cylindrical buffer chamber, and a fiber-optic acoustic sensor. The first-order resonance frequency of the mini-resonant photoacoustic sensor is significantly reduced compared to conventional T-type resonant photoacoustic sensors, achieving a volume of only 0.8 cm³. The sensor was tested using trace methane as the target gas, achieving a detection limit of 101 parts-per-billion at a 100-second integration time, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 1.04 × 10⁻⁸ W·cm⁻¹·Hz⁻¹/². The sensor's performance is superior to previously reported resonant and non-resonant PAS sensors, making it suitable for high-sensitivity miniaturized trace gas sensing in confined spaces. The study also includes detailed simulations and experimental results to validate the sensor's performance, demonstrating its potential for practical applications in various fields such as medical diagnosis, combustion diagnostics, and environmental monitoring.