The energy release rates of fission products have been calculated by summation of the contributions of respective fission product nuclides. An attempt is made to refine the existing values of beta- and gamma-ray energy release rates at short times after fission by including information on more fission products, mainly short-lived ones. In the calculation, 443 radioactive and 125 stable nuclides are considered. The unknown nuclear data for short-lived nuclides are estimated theoretically or statistically. The Q values are obtained by using the semiempirical mass formula of Myers and Swiatecki. The beta-decay constant, λ, of a nucleus is derived from its Q value by using the empirical correlation between λ and Q., Feasibility of the method is evaluated through comparison of the calculated results with experiment. The results are in good agreement with the experimental results for the gamma-ray energy release rates at short times after the fission; usefulness of the estimated nuclear data is thus indicated. The calculated decay powers are in good agreement with the calorimetric measurements of Day and Cannon. The present results of decay power also agree well with the compilations by Shure and by Stehn and Clancy for the respective cooling times.