Abstract. Incharoen T, Nakhen W, Yaemkong S. 2022. Qualitative and quantitative phenotype of Kai Tor-Kai Tang (Gallus gallus) in the lower-northern region of Thailand. Biodiversitas 23: 5387-5395. The Kai Tor-Kai Tang (KT) chicken is a crossbreed between an indigenous domestic village breed and a local wild red junglefowl. Colorful plumage, a crowing voice, and a large single comb are specific characteristics of the phenotype. Due to their populations, there is a clear need to improve the qualitative and quantitative understanding of these chickens. A study of their phenotype variation may be an advantageous approach in the conservation and preservation of the breed, as well as social and commercial utilizations in rural communities. This study aimed to characterize the phenotypes of KT populations reared in the lower-northern region of Thailand, which includes Phetchabun, Phitsanulok, Phichit, Sukhothai, Uthai Thani, and Uttaradit provinces. A total of 100 KT chickens from 35 local farms were characterized under field conditions for 12 qualitative and 2 quantitative traits. Frequencies and means were calculated for phenotypical characteristics. Correlation coefficients and affecting factors factor were evaluated between qualitative traits among them. The results indicated that the most prominent colors of the earlobe, the colors around the eyes, beak, and shank were red (38%), orange (54%), brown (64%), and grey (56%), respectively. The main color of the neck and back plumage was brown-yellow (49% and 31%, respectively), the both long curving tail and back tail was black-green (96%), and the wing plumage color was red (79%) while 49.26%, 99% and 73% of the chickens had Jak Kod Hna comb, normal spur type, and Plod plods scale type, respectively. The overall mean body weight and age of the chickens were 1.07 ± 0.2 kg and 11.99 ± 7.4 months. The highest correlation (r: 1; p<0.01) was observed between the colors of the long curving tail and the back tail. The whole region had a significant effect on long-curving tail and back tail color (p<0.05), and all farm sizes had a significant effect on earlobe color (p<0.05).