Abstract: One kind of non-ionic surfactants(NIS) has been studied by DCIMS together with EIMS and IR.Ammonia was used as the reactant gas and DCI spectrum with high abundant quasi-molecular ions(M+18)~+ has been obtained. From the informations of DCI, EI and IR spectra, the kind of non-ionic surfactants has been identified as polyethoxylated alkyl-phenols. The number of oxyethylene groups and the length of alkyl chain have also been determined.The molecular weight distribution of polyethoxylated alkyl-phenols was obtained from the average spectrum of DCI.Finallly the Origin of the tragments was postulated through the informations from mass chromatograms and further verified by B/E and B~2/E linked scansin the FFR-1. Important information about alkyl chain branching have been obtained from the fragment ion pattern of EI spectrum and B/E linked scan.