Polarization of the 7 3S 6 3PJ radiation from the Hg atom was observed under electron impact with an energy a little above the 6 1S 7 3S threshold excitation energy. The observing direction was perpendicular to both the incident electron beam and the atomic beam. All of the triplet radiation (J = 0, 1 and 2) was slightly polarized. The observed degree of fractional polarization was -3.07, 1.98 and -0.33%, corresponding to J = 0, 1 and 2 spectra in the final 3PJ states of the Hg atom, respectively. These values could be explained by assuming unequal populations in the sublevels Ms = 0 and ±1 of the 7 3S states, deviating from an equal mean value of (1/3) for each sublevel. The deviation value of the fractional population for the sublevel Ms = 0 was 0.348±0.004.