Potential grain yield of rice plant was calculated from potential grain yield of each leaf for two lines of IR 667 and two commercial varieties(Jinhung and Paldal). According to the percentage contribution of each leaf the pattern of potential grain yield of IR 667 lines could be grouped into the upper leaf-dependent type indicating fast senescence while that of commercial varieties could be grouped into the lower leaf-dependent type indicating shade resistance. The comparisons between potential grain yields and apparent grain yields indicate that the commercial varieties having a comparably unfavorable plant type thus remained much behind the potential yield. The significance of potential grain yield was discussed in relation to nutrio-physiology and breeding. Methods for potential yield determination were also discussed.