Conventional Zeeman decelerator, consisting of 80 stages, was constructed and tested. The experimental setup was characterized using O₂ as the reference molecule. Known results of deceleration of O₂ were reproduced. As an extension, detailed REMPI analysis of deceleration of O₂ was carried out, this REMPI analysis was conducted in parallel with ref [1]. Numerical simulation was successful in reproducing the TOF and REMPI spectra of deceleration of O₂. The extension of using Zeeman decelerator to decelerate a polyatomic radical, CH₃, was successful: from initial velocity of 480m/s to a final velocity of 368m/s, corresponding to a removal of 41.2% of the initial translational energy. The decelerator’s efficiency at final velocity of 368m/s is around ~10%. The limiting factor of further deceleration is the signal to noise ratio. Hence, optimization of DC discharge conditions of CH₃ were attempted, but the attempt was with limited success.