Given the importance of drying process in the rice production and in order to obtain the optimum time to achieve moisture balance in the tempering, influence of different drying temperatures (40, 50, 60 and 70oC) and drying time have been studied for four different paddy cultivars (Nemat, Neda, Pagouhesh and Pardis) in the time range of 0.5 to 8 hours at 10 levels of 0.5, 1, 1.5, 2, 3, 4, 5, 6, 7 and 8 hr (as independent variables) in a factorial experimental design based on randomized complete block with three replications. The results obtained in this study indicated that the gradient of the effective diffusion coefficient (K1, as dependent variable) in the early stages of tempering period (after completion of the heating up to one hour of rest) was much more than that of the later tempering stage (from one hour to two-hour relaxation time). The effective diffusion coefficient for the Nemat and Nedacultivers with a similar genotype was larger than that of Pagouhesh and Pardiscultivers. Based on the results obtained in this research, 1-hour relaxation time is recommended at drying temperatures less than 50oC and 2 hours for drying temperatures higher than 50oC. Adsorption and desorption of surface moisture in the relaxation period has a direct influence on grain fracture.