Slow evaporation of a 1 : 1 or 1 : 2 molar solution of p-nit roaniline and p-nitrophenol in a mixture of dichloromethane and n-hexane deposited two kinds of single crystals which were mechanically separated : 2 : 1 molecular crystal A and 1 : 3 molecular crystal B. in a similar manner a 1 : 1 or 2 : 1 molar solution of m-nitroaniline and m-nitrophenol in a mixture of chloroform and petroleum ether deposited the single crystals of 2 : 1 molecular crystal C. The crystal structures of A, B and C were found to be isomorphic to those of p-nitroaniline, p-nitrophenol (b form) and m-nitroaniline, respectively. The characteristics of the crystal structures of A, B and C are discussed.