The CH3S radical was formed from reaction of dimethyl disulfide (CH3SSCH3) with microwave discharged O2 in a flow tube. The Ā 2A′ ← X̄ 2A″ fluorescence excitation spectrum was observed in the wavelength region 615 - 692 nm. The origin was located at 14,542 cm-1; the vibrational frequency for the S-O stretching of the Ā state was 859 cm-1. Dispersed fluorescence was observed in the 680 - 850 nm region. The main progressions gave vibrational frequencies of 1066 cm-1 (ν5″, S-O stretching), 704 cm-1 (ν7″, C-S stretching), and 1464 cm-1 (ν4″, CH3-deformation). The results agree with ab initio calculations. Infrared absorption lines of the CH3S radical were observed after UV photolysis of a CH3SH/Ar (1/500) matrix at 12 K. The results yielded ν1 (C-H stretching) = 2948.6, ν2 (CH3-umbrella) = 1315.1, ν3 (C-S stretching) = 719.4, ν4 ≈ 2873, and 2ν6 (CH3 rocking) = 1154 cm-1.