The mass spectrum for S, Se, and S-Se mixed vapor has been measured. From the dependence of the relative intensity of S-n(+) clusters on the electron-impact energy E(e) it is suggested that neutral S-2 dimer may be evaporated from S-n(+) clusters. The E(e) dependence of the relative intensity of Se-n(+) clusters is more complicated. The spectrum for S-Se mixed vapor suggests that a S atom may be replaced by a Se atom in S-rich clusters.