The aim of the study was to investigate the influence of diet protein level on the metabolic status of fattening pigs as well carcass and meat quality. The research was conducted on 30 crossbred piglets (Landras x Durok), of both sexes, aged about 60 days. Piglets were divided into two groups with 15 animals in each group, where one group was fed with a commercial feed mixture with a lower (16%) and the other with a higher level (18%) of crude protein (SP) in the diet during the entire fattening period. The MAXFERM/PRO in the amount of 400 ppm was added to the feed mixture with a lower protein level (ST_1/16). Animals were weighed individually at the beginning and after 117 days of fattening (end of fattening). Feed consumption was measured daily at group level. Blood samples were taken during bleeding on the slaughter line, and the concentration of N compounds in the serum (total proteins, albumins, creatinine), glucose, total cholesterol, bilirubin, electrolyte concentrations (Na, K, Cl, P, Ca) and serum enzymes activity (gamma glutamyl transferase - GGT, alkaline phosphatase - AP, alanine aminotransferase - ALT, lactate dehydrogenase - LDH) were determined. For each individual pig on the slaughter line, carcass weight, thickness of bacon and muscle tissue, and estimated meatiness of the halves (two-point method) were determined, and after 24 hours of cooling, the pH value of the long back muscle (pH24) and color (CIE L* a* b *). The results showed that feeding to higher final weights (135 kg) with a feed mixture with 16% crude protein with the addition of the MAXFERM/PRO achieves satisfactory production results (daily gain and conversion) and carcass quality (meatiness). The values of metabolic indicators in the blood was not differ from the values of the same in pigs fed with fodder mixtures with 18% crude proteins. The above indicates that the addition of fermentation by-products of certain substrates with the help of fungi such as MAXFERM/PRO to feed mixtures for fattening pigs enables the use of lower levels of protein in the meal without negative effects on the health, production results and meat quality of fattening pigs. The above potentially reduces the excretion of N compounds in feces, and thus has a positive impact on the environment.