The objective of this study was to evaluate the supplementation of L-Arginine in diets with and without dairy products for piglets weaned at 21 days old. Thirty-two animals with initial mean weight of 5.16 ± 1.92 kg and from the same commercial lineage were allocated in a randomized block design to four diets. The experimental diets consisted of a corn and soybean meal-based diet (NDD), the same diet supplemented with 0.6% L-Arginine (NDDA), the diet supplemented with powdered whole milk (DD), and the diet supplemented with powdered whole milk and 0.6% of L-Arginine (DDA). At 43 days old, 16 animals were slaughtered. The productive performance, incidence of diarrhoea, serum parameters, relative organ weight, morphometry and intestinal health were evaluated. Supplementation with 0.6% of L-Arginine increased (P <0.05) the daily and final weight gain of the piglets at 32 days old and reduced the incidence of diarrhoea. DDA promoted a higher villi to crypt ratio (P <0.05). There was a lower rate of mitosis and apoptosis in the jejunum of animals fed DD and DDA. The non-dairy diet supplemented with 0.6% arginine (NDDA) increased serum immunoglobulin A (IgA) and Immunoglobulin G (IgG) concentrations compared with NDD (P <0.05). Thus, supplementation with 0.6% L-Arginine increased immunological activity, improved intestinal integrity, and reduced the incidence of diarrhoea.