Abstract: For the purpose of investigating the most economical and effective sample size for estimating heritability of Pinus yunnanensis in seedling stage, the seedling height and ground diameter of seedlings from 34 half-sib families of P. yunnanensis were randomly selected, and some data were estimated by HalfsibSS 1.0 software to estimate the heritability of various characters under different sample sizes, the analysis of the effect of sample size for trait heritability estimates, determine the minimum sample size required by each trait heritability estimates.The results showed that for the 34 P. yunnanensis half-sib families, different sample sizes had significant effects on the heritability estimates of seedling height and ground diameter. When the sample size of each family was less than 60 individuals, the estimated heritability of seedling height and ground diameter fluctuated greatly, and the standard error was large. When the sample size was more than 60, the accuracy of the heritability increased gradually with the increase of the sample size. Therefore, in this study, more than 60 individuals should be used for the reliable heritability estimation.