Volatilization of selenium (Se) is a dissipation mechanism by which gaseous Se is redistributed in the environment. The vapor pressures of dimethyl selenide (DMSe) and dimethyl diselenide (DMDSe) were determined using the isoteniscope method, and the solubility of DMSe in H2O was determined in a closed system by headspace analysis. The vapor pressures at 25-degrees-C were 32.03 and 0.38 kPa for DMSe and DMDSe, respectively. The enthalpies of vaporization were calculated as 31.90 and 74.92 kJ mol-1, respectively. The solubility of DMSe was 0.0244 g/g of H2O. The Henry’s law constant for DMSe was calculated as 143 kPa kg mol-1 (0.144 kPa m3 mol-1).