This trial was conducted to study the effects and interaction of dietary sodium butyrate (SB) and mannan-oligosaccharides (MOS) on growth performance and immunity in weaned piglets. Seventy-two 28-day-old Landrace×Yorkshire weaned piglets with average weight of (6.68±0.23) kg were divided into 9 treatments with 4 replicates of 2 piglets using a randomized complete-block design, and then were fed diets containing one of nine additives of 0, 0.10% MOS, 0.20% MOS, 0.05% SB, 0.05% SB+0.10% MOS, 0.05% SB+0.20% MOS, 0.10% SB, 0.10% SB+0.10% MOS and 0.10% SB+0.20% MOS. The experiment included adjustment period of 3 d and trial period of 28 d. The results were showed as follows: 1) During 28～41 d, average daily gain (ADG) was increased (P<0.05) and F/G was decreased significantly (P<0.05) for piglets fed with diet containing 0.10% SB+0.10% MOS. During 28～55 d, ADG was increased significantly (P<0.05) for piglets fed with diet containing 0.05% SB+0.20% MOS, 0.10% SB+0.10% MOS and 0.10% SB+0.20% MOS, in which 0.05% SB+0.20% MOS and 0.10% SB+0.10% MOS significantly decreased F/G of piglets (P<0.05). 2) Average daily feed intake of piglets fed with diet containing 0.10% SB+0.10% MOS was higher than that in other groups (P<0.05). 3) On day 7 after injection OVA for piglets, serum’s anti-OVA antibody of piglets fed with diet containing 0.05% SB+0.20% MOS, 0.10% SB, 0.10% SB+0.10% MOS or 0.10% SB+0.20% MOS was increased significantly (P<0.05). 4) No interaction appeared between SB and MOS in improving growth performance and immunity when SB and MOS were combined to use in diet of piglets. In conclusion, growth performance and immunity of piglets were improved by dietary SB or MOS supplementation and 0.10% SB+0.10% MOS was an appropriate and feasible combination, but interaction between SB and MOS was not found in the present study.［Chinese Journal of Animal Nutrition, 2010，22（2）:346-351］