Measurements of the rates of collisional quenching of HgCl∗ (B2 Σ+1/2) by He, Ar, Xe, N2, Cl2, HCl, and CCl4 are reported in this paper. Steady‐state measurements are made of HgCl∗ fluorescence produced by photolyzing HgCl2 using Xe2∗ radiation. A background pressure of [Xe]⩾100 Torr ensures that the HgCl∗ is vibrationally relaxed and all the quenching measurements are from v′=0. He, Ar, and N2 showed no quenching for pressures <1000 Torr. Xe, Cl2, HCl, and CCl4 resulted in two‐body quenching rates of 2.4×10−13, 1.3×10−10, 8.6×10−11, and 1.2×10−10 cm3/sec, respectively. These rates are derived by using an estimated HgCl∗ (B2 Σ+1/2) lifetime of 29 nsec.