A factorial experiment (3×2)   was carried out to study the effects of weaning age (at 4 and 5 weeks old) and dietary β-pro supplementation () 0.0, 0.02 and 0.04%) on growth and carcass traits in fattening rabbits. Seventy two unsexed New Zealand White (NZW)× Californian (CAL) rabbits, weaned at 4 or 5 weeks old, were randomly distributed into six equal groups of four replications, each contained three rabbits. Three experimental diets were fortified with three levels of β-Pro (0.0, 0.02 and 0.04%) and formulated to meet the nutrient requirements of growing rabbits. Rabbits of each replication were weighed, kept in a battery cage, fed their respective experimental diet and managed similarly during the duration of this study. Deaths was monitored and registered daily. Weekly records on live body weight (LBW) and feed intake (FI) were maintained on a replicate group basis, and thus, body weight gain (BWG) and feed conversion ratio (FCR) were estimated. The efficiency of protein (PER) and energy utilization (EEU) and economic efficiency of feeding (EEF) were calculated for the whole experimental period. Some carcass traits were also determined. The results obtained could be summarized as follows: No mortality was observed in the experimental rabbits during this feeding trial. Regardless of dietary β-pro supplementation, delaying weaning age to 5 weeks significantly increased (P≤0.01) total FI and final LBW of rabbits compared with those of rabbits that were weaned at 4 weeks old. Dietary supplementation with β-pro failed to significantly affect the final LBW of rabbits but caused a significant (P≤0.01) increase in total FI and when the level of its addition reached 0.04% total BWG improved significantly(P≤0.01), irrespective of weaning age. Neither weaning age nor dietary β-pro supplementation could significantly alter FCR, PER, EEU or EEF during this study. The interactions between weaning age and dietary β-pro supplementation were not significant (P>0.05) for all growth performance criteria, except for the total FI the interaction was significant (P≤0.01). Carcass traits of rabbits were not affected by weaning age, dietary β-pro supplementation or the interactions between them. Based on the present results, delaying weaning of rabbits to 5 weeks old along with addition of 0.04% β-pro to their diets are recommend to achieve better growth performance, with no adverse effects on carcass traits.