The effect of interaction between solitons on statistical mechanics of a classical sine· Gordon chain is studied. We extend the soliton·gas phenomenology of Currie, Krumhansl, Bishop and Trullinger to include the interaction between solitons. Restriction due to the interaction on the phase space available for solitons is determined andthe second virial corrections are calculated. The interaction' reduces the soliton density and the specific heat, but does not affect the correlation length ofa soliton-sensitive correlation function. These results agree with those obtained by means of the exact transfer integral method.