This study was carried out to determine the fattening performance of Herik lambs reared under in intensive conditions. Twenty single male lambs, all with an mean body weight of 20.78 kg, were used in the study. Concentrate was given ad libitum and alfalfa was given in the amount of 300 g/lamb/day. The lambs were slaughtered when they reached the live weight of 40 kg. In this study, daily weight gain was generally tended to increase between the initial day and 56th day while it tended to decrease from 56th day to the end of fattening. During the fattening, the daily body weight gain and the feed efficiency were determined as 211 g and 9.668 respectively. Also, the temperature humidity index was determined above to accepted threshold value in ruminants along fattening period. Consequently, daily live weight gain and feed efficiency of Herik lambs were worse than those of Turkish native breeds at the slaughter weight of 40 kg.The unsatisfactory in fattening performance of Herik lambs may be depend on exposed high temperature along fattening period and till now lack of improvement studies on them. Thus, researchs should be done for fattening performance of Herik lambs under different breeding conditions.