This study was carried out on the walnut varieties 29/B-4, 170/B-16, 32/B-18 and 198/110 in Tokat province ecological conditions. When research was conducted in 1994-95 walnut trees were 14 years old. The trees were planted with spaces of 10x10 m. No yield was obtained for some years from these walnut cultivars which were planted in 1980. Reasons of insufficient yield were investigated in this study. Important characters determined in the research were canopy growth of the trees, date of budbreak, growth of the shoots, state of flowering, state of damaged terminal shoots by late spring frosts and potential yield indices. State of flowering was protogyny for whole varieties. In addition it was not coincided with male flowers in some trees. The damage rate of terminal shoots by late spring frosts was appeared to be 87.18 % in 1995 while it was 3.59 % in 1994. The potential yield indices in cultivars studied in 1994 were ranged between 235.8-314.3. The potential yield indices could not be calculated in 1995 because of serious frost damages. In conclusion, the most important factors which influence yield, according to importance order were determined to be damage of terminal shoots by late spring frosts, decrease in male flower number, formation of male and female flowers at different time.