Rumen juice transfaunation (RT) has been suggested as one of the effective ways to improve the performance and health of the host. This study's objective was to investigate the effect of RT on behavior, performance and kidney function of fattening lambs. Twelve male lambs were divided into three groups at random: controls (CON, n = 4): lambs were given one liter of normal saline, (Ts, n = 4): lambs received 1 liter of sheep ruminal juice and (Tc, n = 4): lambs received 1 liter of cattle ruminal juice, once throughout the study. Each lamb was caged in a single pen with alive weight of 20.7 (±1.95) and the experiment lasted six weeks. The instantaneous scan sampling approach was used to record behavioral observations on days 1, 2, 3, 7, 8, 15, 16, 30, 31 and 45 & 46 after rumen fluid transfauntion; production parameters and kidney function were measured every week. Rumen juice transfaunation resulted in a significant decrease in chewing pen fixtures behavior especially in Ts and feed conversion ratio in both (Ts and Tc) at first and second weeks, however a significant increase in body weight in both (Ts and Tc) at third, fifth and sixth week compared to control lambs. There was no significant effect on the serum creatinine and urea levels. In conclusion, the current results indicate that RT has a beneficial effect on fattening lamb's behavior and performance; therefore it can be used in intensive fattening sheep farms.