Introduction. Digestive disorders are a major cause of morbidity in weanling piglets. Chlorella and spirulina microalgae have been studied in adult humans because of their antioxidant, antimicrobial and antiviral properties, but information is scarce on their effect on health in young animals. Materials and Methods. A total of 96 weaned piglets were used in a 5-week feeding trial to evaluate the effect of dietary supplementation with chlorella or spirulina on growth, nutrient digestibility, microbiota, and gut health. Piglets were allocated to one of four dietary treatments according to body weight and gender: i) negative control weaning diet without antibiotics (NC); ii) NC+1% chlorella (C); iii) NC+1% spirulina (S); iv) NC+0.02% colistin as a positive control (PC). Piglets received the experimental diet from 28 to 42 d of age, followed by a standard diet. Results and Discussion. Compared to NC, microalgae inclusion did not modify average daily gain, average daily feed intake, and gain:feed ratio. There was no effect of treatment on apparent total tract digestibility of nutrients or on the concentration of volatile fatty acids in the digestive tract. Piglets in group C had the lowest incidence of diarrhea (P<0.05). Plasma concentrations of haptoglobin at 42 d of age did not differ among groups. Villus height at 42 d of age in the jejunum was greater (P<0.05) for piglets receiving diets C and S than for those receiving diet PC. In conclusion, dietary supplementation with microalgae could help protecting the digestive tract of weaned piglets, but the mechanisms of action remain to be identified.