||The enzyme polyphenol oxidase( PPO) has been related to undesirable brown discoloration of wheat based end products such as noodles. 164 cultivars from winter wheat region in China were used to screen grain PPO activity , and 83 cultivars were used to determine flour PPO activity and other quality characteristics. Two sets of wheat samples were used to investigate the effects of genotype, environment and their interaction on grain and flour PPO activity. Significant differences in grain and flour PPO activity were observed in the China winter wheat populations. Grain PPO activity among China winter wheats ranged from 1. 93 to 12. 00 A475/ g min - 1 ×103, and flour PPO activity ranged from 0. 22 to 3. 74 A475/ g min - 1 × 103. The variability in grain and flour PPO activities was influenced by growing location and genotype for the winter wheat samples. The variation in grain and flour PPO activities among growing locations appeared smaller than variation produced by genotypes for the winter wheat samples except for soft wheat flour PPO. Flour PPO activities were related to L3 of flour and 24 h fresh noodle sheets , correlation coefficients were - 0. 50 and - 0. 59 respectively. Quality parameters , such as grain hardness , milling yield , flour protein , water absorption and falling number significantly Correlated with flour PPO activities. Test weight, TKW , grain hardness and flour yield affected PPO content through changing bran content, while protein and starch affected PPO activities.