The purpose of this study was to determine the effects of age at slaughter and sex on carcass characteristics and meat quality of Betong chickens that were raised under a semi-free-range system. A total of 360 chickens from Takbai, Narathiwat Province, Thailand were arranged into 3x2 factorial design with 3 levels of age at slaughter (16, 20, 24 weeks) and sex (male and female) in CRD. The experiment consisted of 6 treatments with 3 replications. Ten chickens of each replicate from each treatment group were randomly sampled for carcass yield and meat quality. Results showed that slaughter and carcass weights were significantly higher when the age at slaughter increased (P<0.01). Males had heavier slaughter and carcass weights (P<0.001) with lower breast percentage than the female chickens in each particular age. Higher yellowness value was significantly illustrated when the age of chickens increased. This color value was higher in both breast and thigh meat of the female chickens (P<0.05). Considering texture analysis, the males had significantly higher shear force value than the females (P<0.05). This shear value tended to increase when the age of the chicken increased (P>0.05). There was no significant difference observed between age at slaughter on chemical composition (P>0.05). Nevertheless, the males had less fat content in breast meat and higher collagen content in thigh meat than the female Betong chickens (P<0.05). The results show that males should be slaughtered at 20 weeks, while the females should be slaughtered when they reach the age of 24 weeks.