An intense Raman spectrum of diethyl disulphide and its polarisation characters are recorded. The spectrum consists of twenty-seven lines. Nine of these are observed for the first time. It is shown that nine of these lines (three of which are depolarised) belong to the ethyl group (C2 H5), and the remaining eighteen of which six are depolarised belong to the chain C2-S-S-C2. The results are discussed in relation to the problem of ‘free rotation’ about the S-S bond. It is concluded that six polarised lines are due to thetrans and twelve due to thecis forms; and that these two types of molecules co-exist in the liquid in equal proportions.