The effect of feeding different levels of yeast on growth performance, blood constituents, and economic efficiency was studied. An experiment was conducted on 300 one day old chicks. There were 3 dietary treatments each consisting of 5 replicates with 10 chicks in each replicates. The treatments were 0% control, 0.2 and 0.4% Brewer's yeast respectively. The data were obtained for body weight, daily gain, feed intake feed conversion ratio during the experimental period. At the end of experiment concentration of protein, glucose, cholesterol, total lipids, phospholipid in serum and haemoglobin were evaluated.  Also different dressing percentages were evaluated.  results showed that chicks fed 0.4% yeast had higher body weight gain (BWG), feed intake (FI)and better of feed conversion ratio(FCR). Chicks fed ration containing 0.2 and 0.4 % of yeast increase in serum phospholipidand total protein of their concentration. Also total variable cost, total costs and total returns (LE/bird) were high in groups feeding 0.2 and 0.4% brewer's yeast Finally we may concluded that from blood concentration parameters that feeding brewer's yeast had low percentages for total lipids, cholesterol and high concentration of total protein and glucose. Economic parameters showed that high net profit was in 0.4% than those of 0.2 of brewer's yeasts. Cobb breeds was preferred than Hubbard breeds from measures of blood parameters and economic efficiency.