AbstractInfrared and Raman spectra ofO, O‐diethyl phosphorodithioic acid have been studied both at and below room temperature. The results show that the vibrations of P=S, P(‐O)2, P‐S and S‐H groups give multiple bands and the relative intensities of these bands vary as the temperature of the sample changes. According to the experimental results, we suggest that there are four rotational isomers ofO, O‐diethyl phosphorodithioic acid. Reasons for splitting the vibrational bands of these groups are also