Determination of sample size for study of some characters in soybeans NguyÔn ThÞ Lan1 Summary Agronomic scientists accept standard error for almost characters at 1 percent, 5 percent or 10 percent. In the present experiment with soybean it was found that the standard error depended on stability of the characters and sample size. The sample size was suggested at 30 and 70 for plant height and pod number per plant, respectively. For determining 1000 seed weight with the standard error below 1 percent three replicates of 500 seed sample size have been suggested. Keywords: Soybean, standard error, sample size.