This paper aimed at determination of the effects of final body weight on the crude fat fraction and fatty acid profile in breast and leg muscles of 42-day-old broiler chickens. ISA 215 chickens were reared up to 42 days of age and identically fed complete diet mixes for broiler chickens, which were called ‘starter’, ‘grower’ and ‘finisher’ mixes. On day 42 of the experiment, a total of 30 chickens weighing 1.5 kg, 2.0 kg, aftd 2.5 kg were selected from each weight group (5 males and 5 females per group). After the slaughter and a 24-hour cooling of the carcasses at +4°C, we determined the fraction level of crude fat and the profile of higher fatty acids: C14:0, C16:0, C16:1, C18:0, C18:1, C18:2n-6, gC18:3n-6, C18:3n-3, CLA, C20.0, C20:4n-6, EPA (C20:5n-3), and DHA (C22:6n-3) in breast and leg muscles of the chickens. The results were analysed statistically with the use of a variance analysis and Duncan’s multiple range test. The experiment did not show any effect of body weight on the level of crude fat in breast and leg muscles of the chickens at the age of 42 days. From the consumer’s point of view, the breast muscles of chickens weighing 2.0 kg showed the most beneficial fat composition because it contained a higher proportion of n-3 acids including a long-chain, unsaturated EPA & DHA, and arachidonic acid (C20:4), as well as because this fat type had the highest unsaturated / saturated acids ratio. The highest level of hypercholesterolemic saturated fatty acids was found in the both muscle types in the chickens weighing 1.5 kg, that appeared to grow at the poorest. There were significant differences in the profile of higher fatty acids between the breast and leg muscles.