This study was designed to evaluate some physiological responses to dietary betaine levels s in broiler chickens. One hundred and twenty, one-day-old unsexed chicks, of Cobb strain, were used in experiment period of 6 weeks.. The birds were allocated in four treatments,30 birds each (3 replicates of 10 birds). Treatments were:T1 as control group (C); T2,Diet C plus 0.01% betaine; T3, Diet C plus 0.02% betaine; T4, Diet C plus 0.03% betaine. Feed intake and body weight per replicate were recorded weekly, Body weight gain (BWG) and feed conversion ratios (FCR) were calculated. At the end of the experiments samples of chickens were randomly chosen and slaughtered to determine dressing percentage and blood samples were taken to measure serum Glucose, Cholesterol, Triglyceride, Total lipids, T3, T4 and Albumin.The results showed that using of 0.03 % betaine of broilers diet had significant differences on BWG, FI, and FCR compared with other groups at 3 and 6 wks of age. The carcass weight was significantly (P<0.001) improved in 0.02 % Betaine. There were a significant increase (P<0.01) in serum total protein, albumin, and globulin concentrations of birds fed 0.03 % betaine levels compared to other treatments. The results concluded that using of 0.03% dietary betaine showed beneficial of some physiological and productive responses of broilers chickens.