The method to determine the decomposition starting temperature of hydrocarbons adsorbed on a single crystal surface was developed by taking use of inhibiting effect of CO on decomposition. The representative results for cycloheptane decomposition on Ni(755) have been presented. Temperature programmed desorption (TPD) spectra after preflash and postdosing of CO indicated that the decomposition of adsorbed cycloheptane to partially dehydrogenated intermediates started at 162 K and was completed by 200 K. The characteristics and differences in predosing and postdosing effects between CO and bismuth have been discussed.