Proguanil is a synthetic biguanide derivative of pyrimidine. It is widely used in chemoprophylaxis of malaria. It is chronically administered for malaria prophylaxis in sickle cell patients and in pregnant women in Nigeria. During the process development or degradation of Proguanil hydochloride, some of the related substances (impurities) were observed. These impurities were identified as 1-cyano-3-(1-methylethyl)guanidine (Impurity A), 1,5-bis(4- chlorophenyl)biguanide (Impurity C) and 1,5-bis(1-methylethyl)biguanide (Impurity D). Present work describes the synthesis and characterization of these impurities.