Abstract: This study was undertaken to evaluate the effect of different dietary levels of Canola Meal (CM) on growth performance and histological responses of broiler chicks. Cobb-500 day-old chicks were randomly distributed to five equal treatments, each of three replications. Ten starter and grower CM-diets (0.0, 10, 12.5, 15 and 20%) were formulated and used for 6 weeks. The chicks were kept in brooding and rearing batteries and fed their respective experimental diets. All chicks were managed similarly. The criteria of response were performance, carcass traits, plasma thyroid hormones and histological characteristics of liver and thyroid. Feeding CM-containing diets (up to 15%) did not adversely affect growth performance or carcass traits but relative weight of thyroid was significantly increased. Increasing dietary CM level up to 20% caused significant increases in feed intake, percentages of abdominal fat and thyroid gland but negatively affected weight gain, feed conversion ratio, bursa relative weight and plasma thyroxin concentration compared with the control chicks. Plasma level of triiodothyronine and activity of alanine aminotransferase were not affected by dietary treatments. Activity of plasma aspartate aminotransferase was significantly increased in chicks fed the highest two levels of CM compared with the control ones. The chicks fed the 20% canola meal diets exhibited progressive changes in the liver architecture and thyroid structure. Taking the histological feature of liver and thyroid, plasma thyroid hormones and growth performance into account, it could be concluded that canola meal can safely be included in broiler diets at a level of 15%.