An analysis was carried out to study the performance of straight rectangular fin with the psychometric correlations given by Hyland and Wexler when subjected to simultaneous heat and mass transfer. Numerical solutions are obtained for the fin efficiency and 2-D temperature distribution with SOR method when the fin surface is dry, fully wet and partially wet. The result was compared with those of previous studies in released literature. The effect of fin parameters including the ratio of fin width and fin thickness to fin length as well as Bix on fin efficiency was also studied. It is found that the temperature distribution on the fin is really two-dimensional and the change of fin parameters shows impressive effect on fin efficiency and 2-D temperature distribution.