The drying behavior of prawn and chelwa fish (Indian minor carp) has been studied under open sun drying (OSD). The drying rate curves contained no constant rate period and showed a linear falling rate throughout the drying process. An asymptotic regression precisely represents the open sun drying behavior with the coefficient of determination and mean square of deviation as 0.9996 and 0.33 x 10(-4) for prawn and 0.9993 and 0.58 x 10(-4) for chelwa fish, respectively. Effective moisture diffusivity values were estimated from Fick's equation. The hourly effective moisture diffusivity has an exponential relation with the hourly mean moisture content of fish. The average effective moisture diffusivities were 11.11 x 10(-11) and 8.708 x 10(-11) m(2) s(-1) for prawn and chelwa fish drying, respectively. (c) 2006 Elsevier Ltd. All rights reserved.