This study was carried out to determine the effect of whole cottonseed (WCS) supplementation on finishing performance and blood parameters of Awassi lambs under heat stress. The compositions of diets for the various treatments were i) control: concentrate without WCS plus 15% wheat straw; ii) 8.5% WCS, 76.5% concentrate and 15% wheat straw; and iii) 17% WCS, 68% concentrate plus 15% wheat straw. Twenty seven male Awassi lambs (4 – 5 months old) were allotted to three dietary treatments in equal numbers for each diet in a completely randomized design. Following 15 days of diet adaptation, lambs were fed the experimental diets ad libitum for 56 days. According to the finishing trial, average daily gain (ADG), feed intake (FI), dry matter intake (DMI), feed efficiency and water consumption were not affected by the inclusion of WCS. Only numerical increment of daily gain, FI and DMI was observed in the 8.5% WCS group. Supplementation of WCS did not affect blood glucose, urea, total protein, albumin and potassium levels, but blood cholesterol level was increased. Changes in scrotal circumference were observed with supplementation of 17% WCS. As a result, WCS can replace concentrate up to 8.5% of diet without negative effects on finishing performance of Awassi lambs under heat stress conditions.