BACKGROUNDː The mechanisms underlying the metabolic effect of surgical treatment for morbid obesity are still unclear. Furthermore, the hormonal and metabolic response to the promising and less-invasive version of Roux-en-Y gastric bypass (RYGB), i.e. mini gastric bypass (MGB), is poorly known. The aim of this study was to evaluate pre- and postprandial changes in peptide YY (PYY) and metabolic parameters in obese patients without diabetes and cardiovascular complications treated by both versions of gastric bypass. METHODSː Venous blood for PYY and other assays was collected three months before and six months after bariatric operation (MGB and RYGB), in the fasting state and two hours after the consumption of a standard 300-kcal mixed meal (Nutridrink Standard, Nutricia Advanced Medical Nutrition, part of the Danone company, Schiphol, The Netherlands). RESULTSː In the MGB group, elevated concentrations of the PYY has been detected both fasting and postprandially. The effect of the MGB on the PYY levels did not differ from the RYGB group outcomes. CONCLUSIONSː The results of our study suggest similar endocrine and metabolic effects of MGB and RYGB procedures. Long-term efficacy and metabolic benefits of MGB require further research.