Abstract: To determine the effects of group size and toys on production performance and stress level in growing pigs, six hundreds and fortyeight White×Landrace female growers with similar initial weight (26.32±0.98) kg and age were randomly allocated into four groups by two factor design of group size (18 and 54 pigs·pen-1) and toys (no provided and provided) for 35 days. For all the trial pigs, space allowance was 0.96 m2·pig-1, with one drinker per 9 pigs and 7.8 cm feeder allowance per pig. The result showed that the production performance was not different among all the treatments (P>0.05). Over the entire period of the trial, large groups had less pollution proportion of the pens than that of small groups (P<0.05).Toys decreased saliva cortisol concentration at day 3 of the trial (P<0.01). Neutrophil: lymphocyte ratios (N/L) also differed and the pigs with large-group or toys had low N/L value (P<0.01, P<0.05). It was concluded that large group or toys could reduce stress level and improve welfare to some extent with no difference in production performance in the pigs, and that large group also decreased the polluted proportion of the pens.