Abstract: Hepatitis C virus (HCV) is one of the leading known causes of liver disease in the world. The HCV is a single-stranded RNA virus. The genomes of HCV display significant sequence heterogeneity and have been classified into types and subtypes. So far, 11 have been recognized with each type having a variable number of subtypes. It has been confirmed that 90% approximately of the isolates HCV infections in Egypt belong to a single subtype (4a) (Ray, S.C., R.R. Arthur, 2000). In this paper, we construct a stochastic model to study the spread of HCV-subtype 4a amongst the Egyptian population. Also the relation between HCV-subtype 4a and the other subtypes is been studied. Also the effect of the mutation factor in the persistence of the disease is been addressed. In this paper we use the method of the stochastic partial differential equations given in (Kapur, J.N., 1988), (Kapur, J.N., 1992) and (Herbert, J., V.S. Isham, 1998), to derive our stochastic model and 02int hen try to solve this model. Threshold conditions for the value of the transmission rates k and k 1 01 02t erms of R , R and the mutation factor have been determined. Also Monte Carlo simulations have 1b een conducted for this disease using the infection rates k and k as random numbers