Background: Malnutrition is a significant problem in those undergoing peritoneal dialysis (PD). Factors such as gastrointestinal (GI) symptoms and the need for a fluid reduced diet can limit tolerance and thereby the efficacy of oral nutritional supplements to treat malnutrition. Objectives: To evaluate the acceptability and impact of two different forms of oral nutrition supplementation for 16 weeks on nutritional markers and quality of life of malnourished patients undergoing PD. Design: A randomised, within-subject cross-over study. Patients assessed as malnourished or with serum albumin <35 g/l were recruited. Participants were randomised to receive either 200 ml of a 1.25 kcal/ml nutrition supplement or a high protein nutrition supplement bar, for eight weeks. Each group then crossed over to receive the alternative supplement for eight weeks. Total intervention time was 16 weeks. Serum albumin, serum transthyretin and food intake were evaluated at baseline, at 8 and 16 weeks. Subjective Global Assessment, the presence of GI symptoms and quality of life were evaluated at baseline and 16 weeks. Results: Sixteen weeks of nutritional support was associated with statistically significant improvements in weight and a reduction in the proportion of patients who were malnourished. There was no difference in the impact of bars compared with liquid oral nutrition supplementation. Patients preferred the fluid supplement to the bars. Conclusion: Sixteen weeks of nutritional support improved nutritional status in malnourished patients on PD.