Since the pattern of the frequency distribution of a parasite within a host showed an overdispersed pattern, various statistical models such as Poisson, negative binomial and lognormal distributions have been applied on the population dynamics in host-parasite relations. The observed data on the number of metacercariae of Clonorchis sinensis in a suitable intermediate host, Pseudorasbora parva which were collected from an endemic area, Juk-Rim River, Kim-Hae Goon, South Kyong-Sang Do were applied on the statistical models. The results obtained are as follows: By the calculation of the raw data, 258(94.9 percent) out of 272 fish showed positive to the metacercarial infection of C. sinensis. The mean number of metacercaria in a fish was 335.1. The standard deviation was 250.6 and the mode was observed between 250 and 299. The frequency distribution pattern of metacercariae of C. sinensis within the fish host in surveyed area was fitted to the lognormal distribution (0.05
