Proteins are large complex macromolecules. The specialized roles of the proteins are very important for many functions in the cell and cell growth is regulated with many signaling pathways that stimulate protein synthesis. During the lifetime of mammals, the protein homeostasis become progressively impaired, causing the weakening of most cellular functions, resulting in diseases associated with aging and death. In this work was determined the protein homeostasis in primary fibroblasts isolated from the skin of wild-type mice and Sti-heterozygous mice. Sti-heterozygous mice are carrying the mutation of the enzyme alanyl-tRNA synthetase which caused incorporation of amino acid serine instead of alanine in its protein. In order to determine the protein homeostasis in primary fibroblasts isolated from mice that are 3 and 6 months old, protein synthesis intensity was determined by measuring the amount of an alkyne analog of puromycin incorporated in the newly synthesized protein. The amount of protein aggregate was determined using a compound that binds the aggregated proteins by the immunofluorescence analysis. The results showed no differences in the intensity of protein synthesis in isolated fibroblasts from the skin of wild-type mice and Sti-heterozygous mice in age 3 and 6 months. However, it was showed that there are higher amounts of aggregated proteins in fibroblasts isolated from the skin of Sti-heterozygous mice in age 3 and 6 months compared to wild-type mice of the same age. The results indicate that protein homeostasis is impaired throughout defects in protein synthesis.