The photodegradation of thiobencarb technical by UVC ( λ=254) was studied to investigate the degradation of thiobencarb after exposure to UVC light for 144 hours, in addition to identification of some by-products by GC/MS. The obtained results showed that, the rate of degradation of thiobencarb was fairly fast so the loss percentage was increased to reach 71.57% after 144 hours and the half-life (t_0.5) was 4.95 hours.  Analysis of samples after exposure to UVC light using GC/MS identified three by-products: thiobencarb sulfoxide, S-4-chlorobenzyl acetyl (ethyl)thiocarbamate and S-benzyl diethylthiocarbamate.