Abstract: Data from 10 year old 6×6 half diallel progeny test of slash pine (Pinus elliottii), across two test sites, were used to estimate the genetic parameters for height, diameter at breast height, volume, wood density, stem straightness, and wind resistance. There was greatly significant difference between test sites for all traits examined, except wood density. Interaction effect between sites and crosses also existed to a certain extent for all traits, and the effect was significant for diameter at breast height and density, the ratios of additive variance to total genetic variance were from 96 41% to 100% for diameter at breast height, volume, straightness, density, and resistance, when mean square of general combining ability (GCA) was significantly greater than that of specific combining ability (SCA). But the result was not similar for height. GCA effects were the main genetic factor to control the performance of full sib families. SCA and reciprocal effects affected the performance of full sib families as well, but the degree was lower. The individual heritabilities of narrow sense were 0.001 and 0.074, 0.080 and 0.144, 0.068 and 0.137, 0.108 and 0.609, 0.052 and 0.252, and 0.058 for height, diameter at breast height, volume, density, straightness, wind resistance (only single site), respectively, across two sites.