Forty eight piglets with initial body weight of 5.60±0.75kg, weaned at 21days of age were used to investigate the effects of diet protein source on their behavior and performance after weaning. The piglets were distributed in a completely randomized experimental design, composed of three treatments (a control diet with soybean meal and maize, diet with nonfat dry milk powder and diet with spray-dried plasma), and four replications, with four animals per experimental unit. The piglets' behavior activities were registered and analyzed through the observation of the videos and registered in a work schedule. These images were analyzed continuously, using the “focal” technique. The animals submitted to a control diet demonstrated during the whole period of evaluation a higher incidence of nosing behavior, less time spent at the feeders more time spent with the manifestation of non-desirable agonistic behaviors (P<0.05) than other treatments. The values for feed intake and weight gain, for animals submitted to control diet were lower when compared to animals submitted to plasma and milk powder diet (P<0.05). It is concluded that piglets weaned at 21days of age and fed with simple diets (control diet), based on corn and soybean meal, demonstrate higher incidence of undesirable behaviors and lower growth performance than the piglets that are fed with diets containing spray-dried plasma or nonfat dry milk powder.