ABSTRACT Objectives: to evaluate undergraduate nursing students’ knowledge about intestinal ostomies before and after an educational intervention via an online platform. Methods: before and after one-group type quasi-experimental research, carried out with 90 undergraduate nursing students from two higher education institutions in Piauí, from July to October 2014. For knowledge assessment, an instrument validated in Brazil was used. Nonparametric inferential statistics was used to compare the pre-test and post-test averages. Results: there was an increase in the average number of correct answers for undergraduate students after intervention in the online educational platform, from 23.67 (SD = 5.9) in the pre-test to 32.01 (SD = 2.72) in the post-test, and this difference was statistically significant (p = 0.000). Conclusions: intervention via online educational platform is considered applicable for teaching undergraduate nursing students on intestinal ostomies.