Abstract: 108 healthy male chickens (5 wk old) with similar body weight，from Arbor Acres (AA) and Beijing-You (BJY) respectively were used to study the effects of chronic heat stress on meat quality and contents of the flavor substances in breast muscle. Chickens from each stock were randomly alloted into 3 treatments: constant high ambient temperature at 34 ℃ with ad libitum feeding (34AL)， constant optimal ambient temperature at 21 ℃ with ad libitum feeding (21AL)， and constant optimal ambient temperature 21 ℃ but pair-fed to the amount consumed by the 34AL group (21PF). All birds were reared in 3 environmental chambers until the end of the trial at 8 wk of age. The results showed that exposed to the heat of 34 ℃ for three weeks， AA broilers exhibited higher L* values and drip loss in breast muscle(P<0.05)， moreover， they showed decreased content of insine monphosphate (IMP) (P<0.01). For BJY chickens， heat exposure had no significant influence on meat quality traits (except for pHu) and contents of IMF and IMP in breast muscle (P>0.05). The data indicated that chronic heat exposure (34 ℃) had a detrimental effect on meat quality traits of breast muscle in AA broilers， while BeijingYou chickens had higher adaptability to high temperature， their muscle fibers were insensitive to heat exposure (34 ℃).