Pecan is one of the most important nut fruits of subtropical regions that has very high commercial value. In this research, chilling and heating requirements of 16 pecan cultivars (GraTex, Peruque, Comanche 4M, 10J, Wichita 6J, Mohawk, Mahan, Stuart 2J, 3J, Stuart 4J, GraKing, Choctaw, Apache, 6M, Wichita 7J, and Comanche 5M) were carried out at the Saidabad Agricultural Research Center of Dezful during 2014–15. The Utah model and chilling treatments of cuttings were used to determine chilling requirement of cultivars. Heat requirements were determined by growth degree day (GDD) method.The experiment was a randomized design factorial with 16 cultivars and 11chilling treatments for 0, 150, 300, 450, 600, 750, 900, 1050.1200, 1500 and 1800 hours at 4°C±1 and three replications. To calculate the chilling requirement of pecan cultivars in natural conditions, meteorological data of Safiabad station were used. The results showed that chilling requirement was lower than 200­h for 'GraKing', 'Wichita 6J' and ‘Wichita 7J’ and higher than 800­h for 'Comanch 5M' and heat requirement were 416­GDD for 'Apache' and 625­GDD for 'Comanch 5M'. In all of cultivars, heat requirement varied inversely with chilling accumulation hours and they required at least 500­h with >18ºC heating for spring budbreak. Finally, results of this study showed that 'Wichita 6J', 'GraKing', ‘10J’ and ‘Apache’ were suitable for subtropical regions of Iran with 300­h chill units and 'Comanch 5M', ‘GraTex’ and ‘6M’ were suitable for regions with 400-600­h chill units.