This study investigated the effects of dietary protein levels and betaine supplementation on nutrient digestibility and performance of Japanese quails. In total, 765 Japanese quails were randomly assigned to a 3×3 factorial arrangement, with five replicates of 17 quails each. Three basal diets were formulated to contain three crude protein levels (16.5, 18.0, and 19.5%). Each protein level was supplemented with 0, 0.06, and 0.12% betaine. The diet with 16.5% dietary crude protein with no betaine supplementation resulted in the lowest crude fiber digestibility, while the 18.0% CP diet supplemented with 0.12% betaine generated the highest crude fiber digestibility (p<0.05). The diets with 18.0 and 19.5% crude protein increased crude fiber digestibility, but reduced ether extract digestibility (p<0.01). Moreover, betaine supplementation increased dry matter, crude protein, crude fiber, and crude ash (p<0.01) digestibility and tended to increase ether extract digestibility (p=0.09). The increase in egg weight for the 18.0 and 19.5% protein diets was correlated with a decrease in feed conversion ratio (p<0.05). However, feed intake and egg production were not affected by protein levels. Betaine supplementation enhanced all performance variables (p<0.01). The diets with 18.0 and 19.5% crude protein resulted in heavier yolks and eggshells than the 16.5% crude protein diet (p<0.05), whereas betaine supplementation increased yolk, albumen, and eggshell weight (p<0.01). The 18.0 and 19.5% protein diets produced similar responses in most evaluated parameters. Laying Japanese quails can be fed diets with 18.0% crude protein. Moreover, betaine supplementation provided several benefits, and particularly improved nutrient digestibility, performance, and egg quality.