Mercuric chloride is very commonly used as disinfec tant in biological laboratory. The study was perfor med to evaluate the effect of mercuric chloride at differe nt concentration on the mixed culture. Contact time was considered as influence parameter, and spread plating-plate co unting was used as numeration method for bacteria concentration. The result showed that as time and c oncentration of disinfectant increased, the growth of culture decreased, which revealed its sterilization efficie ncy. The disposal of used mercuric chloride from th e laboratory cause environmental hazard, thus the proper measure should be taken before its discard.