The experiment detected the chill hour requirements of 6 female and 8 male varieties of Pistachio (Pictacia vera L.) cultivated in Aleppo, Idleb, Hama and Dar’a in Syria needed to break down their bud dormancy. Studied cuttings left at 2°C in cool chamber for 650, 750, 850, 950, 1050 and 1150 hours were placed into growth chamber offering temperature, moisture and brightness similar to those available in nature during the period of blooming flowers. Statistical analysis distinguished clearly between the chill requirements of the female and the male varieties, where the males needed lower cold hours. Also, the female varieties showed differences among them in their chill requirements due to genetic resources which were affected by their geographical areas and attitudes. The period in the growth chamber needed to reach a proper blooming ranged between 32 days in the case of Ashoury variety cultivated in Dar’a with 1150 chill hours and 54 days with Nab Aljamal variety existed in Hama and Idleb with 650 chill hours. Meanwhile, in the male varieties this figure was between 22 days for male 2 cultivated in Idleb (1150 chill hour) and 43 days for Male E in Dar’a (650 chill hours). The cluster configuration between the males and females varieties was sorted by putting them in two relative distant sub-clusters. The females varieties were distributed sorted into sub-groups as well, insuring the similarity among the ones belong. In addition, The males varieties were distributed into two types depending on their earliness blooming time (early: Hama1, Hama2, Idleb1, Idleb2 – late: A jellin, E Jellin, Aleppo1, Aleppo2). The results could be useful for the decisions of what varieties to be grown in certain places depending on natural chill hours available there.