This experiment was carried out to investigate the relationship between grain shapes and ecotypes in Korean native weedy rice. The 111 lines of Korean weedy rice were classified into japonica (91 lines) and indica (20 lines) by RAPD analysis, which was reported in 2005 (Chung and Ahn). The characteristics of grain shape such as grain length, width, thickness, 1,000 grain weight, the ratio of length to width (L/W), the ratio of length to thickness (L/T), and the ratio of width to thickness (W/T) were measured in each ecotype, and their statistical distributions were compared by t test. The mentioned 7 characteristics were significantly different between japonica and indica weedy rice groups, but these could not classify weedy rice accessions into two groups without exceptions according to the classification by RAPD analysis. Out of variables concerning grain shape, the L/W was the highest distinctive to separate ecotypes. A critical point of L/W to divide ecotypes was calculated from the mid point between upper critical limit of japonica and lower critical limit of indica in confidence interval at α=0.05. At critical point of L/W = 2.138, decision error was 2.2% in japonica group, and 5.0% in indica group. Conclusively, the classification of ecotypes by L/W of grain made almost (under 5% error) same result with that by RAPD markers in Korean native weedy rice.