The purpose of the study was to assess the fattening parameters and carcass quality traits of fatteners after replacing soybean with varying proportions of peas and yellow lupin in the mixture. Sixty fattening pigs (50% gilts and 50% barrows, with an initial body weight of approximately 31.60 ± 3.01 kg) were divided into three feeding groups: control (C) – standard feeding with 100% post-extraction soybean meal in the first and second fattening phases; experimental group (E1) – 50% of the protein sources were replaced with peas and lupin in the first fattening phase, and increased to 75% in the second phase; experimental group (E2) – 50% of the protein sources were replaced with peas and lupin in the first phase, and soybean was fully replaced by peas and lupin in the second phase (100% legume protein). Fattening performance and slaughter characteristics of pigs were evaluated. Daily weight gains of fattening pigs were similar in all groups, as was feed intake, with each group consuming just over 3 kg of feed per kg body weight gain. There was no significant impact of the diet on meatiness, which was above 56%. The average fat thickness from 5 measurements, and the values of individual measurements in various carcass sections, were also consistent among the groups. The study demonstrated that peas and lupin could partially or fully replace soybean meal in fattening pig diets without negatively affecting fattening performance or carcass quality, particularly in the final phase of fattening.