Slaughter guinea fowl are not produced in Poland on an industrial scale, but the demands of the meat market can change at any time to meet consumer demand or in reaction to expanding markets. The objective of the study was to determine the effect of age of the birds on slaughter yield and their meat quality. No effect of the bird’s gender was included as young guinea fowls showed no distinct sexual dimorphism. The study involved guinea fowl fed on full-portion mixtures containing no antibiotic growth stimulator; the birds were reared up to the 18th week of life. The bird slaughter was performed on week 14, 16, and 18 of life, and 10 birds were slaughtered in each of the three terms, and at the same time, the following factors were determined: slaughter yield, composition, pH, and chemical composition of breast and leg muscles. Mean weights of the guinea fowl bodies were: 1181 g, 1314 g, and 1373 g, respectively in the subsequent slaughter terms 14, 16 and 18 weeks of life. The slaughter yields of the guinea fowls, regardless of their ages, were similar and ranged from 73.61 to 74.49%. The guinea fowls slaughtered on week 14 of life had the highest per cent contents of breast, thigh, and leg muscles; they were 17.66% 10.23%, and 6.13%, respectively. The pH of muscles decreased with bird age and pH of leg muscles was always higher than pH of breast muscles. The content of total protein in breast muscles ranged from 23.72 to 26.37% and in the leg muscles: from 21.04 to 23.20%. The fat content ranged from 0.84 to 1.12% and from 2.38 to 5.86%, respectively. The results of this study indicate that the slaughter guinea fowl rearing period should be completed on, approximately, week 14 of life.