The prime objective of the present numerical study is to analyze the thermal performance characteristics of an absorber plate fin of a sheet and tube type solar flat plate collector of fixed collector area. Considering temperature dependent thermal conductivity and overall loss coefficient and assuming cubic temperature profile along the tube, pseudo-transient form of two-dimensional, highly nonlinear partial differential equation governing the steady state temperature distribution in the absorber plate fin is solved using Alternating Direction Implicit finite difference scheme. Keeping ambient temperature, fluid inlet temperature and number of tubes fixed, numerical results are presented and discussed for wide range of values of aspect ratio of the absorber plate, fluid outlet temperature, overall loss parameter and solar flux. Finally, it is found that there exists an upper limiting value of solar flux beyond which increase in heat transfer rate is insignificant. Further, it is concluded that fin efficiency remains independent of aspect ratio of absorber plate whereas it increases significantly with decrease in overall loss parameter and decreases slightly with increase in fluid outlet temperature. (C) 2015 Elsevier Ltd. All rights reserved.