The instantaneous distribution of chain composition for random terpolymers has been derived by adopting a similar strategy to that used by Stockmayer. The analytical result shows the same Gaussian behavior for the random terpolymer distribution. When the concentration of the third comonomer is low and they are almost individually dispersed along the chain (the quasiterpolymer case), the explicit distribution is given by (the Stockmayer’s copolymer result)*(wt)(t), where t and w are the concentration and the relative probability of incorporating the third comonomer within a chain.