Abstract: Proportions of full seeds in outcrossed cones,self pollinated cones,and open pollinated cones in 1993 and 1994 was used to estimate outcrossing rate of a masson pine clonal seed orchard.It was found that there existed higher selfing rate in the masson pine clonal seed orchard at age 8 or 9.The great differences were found between clones from various parents for outcrossing rates under open pollination,which ranged from 44.7% to 98.1% (av.73.5%±17.3%) in 1993,and from 30.8% to 96.8% (av.69.2%±21.3%) in 1994 respectively.The outcrossing rates were larger among combinations within clones than among clones.The coefficient of variability of the former was 35.3% to 53.0% of the latter.No significant differences were observed for outcrossing rates of the same combinations between two years.Meanwhile,the crossing rates were found to be significantly and positively related to the fertilized cone rates.Finally,main factors affecting crossing rate was discussed.