This study aimed to quantify collagen fibers in different lineages of country chicken at different ages and anatomical regions. The collection of material was carried out in both lineages (five poultries/treatment) at two different times: 42 and 72 days of age. At each moment, a fragment of the pectoralis thoracic (PT) and lateral iliotibial (LIT) muscles was collected, which were fixed in 10% formaldehyde for 48 hours; they underwent a conventional histological approach, they were stained with picrosirius, and they were measured through the morphometry software KS-400 ZEISS®. The quantity of collagen fibers found in the muscles collected at 42 and 72 days, regardless of the region under study, was, respectively, 2.32±2.31% and 4.56±2.94%, for the Label Rouge lineage, and 2.26±1.61% and 4.92±2.12%, for the Pedres lineage. The quantity of collagen fibers in the different lineages and anatomical regions showed no significant statistical difference. However, when age (42 and 72 days) was taken into account, a significant statistical difference was observed. The increased amount of collagen fibers found in the lineages under study is influenced by age and it’s probably one of the factors which can influence meat texture.