Measurements of the rates of collisional quenching of HgCl* (B2 &Sgr;+1/2) by He, Ar, Xe, N2, Cl2, HCl, and CCl4are reported in this paper. Steady‐state measurements are made of HgCl* fluorescence produced by photolyzing HgCl2using Xe2* radiation. A background pressure of [Xe]⩾100 Torr ensures that the HgCl* is vibrationally relaxed and all the quenching measurements are fromv′=0. He, Ar, and N2showed no quenching for pressures <1000 Torr. Xe, Cl2, HCl, and CCl4resulted in two‐body quenching rates of 2.4×10−13, 1.3×10−10, 8.6×10−11, and 1.2×10−10cm3/sec, respectively. These rates are derived by using an estimated HgCl* (B2 &Sgr;+1/2) lifetime of 29 nsec.