The aim of the study was to estimate the usefulness of measuring the thyroglobulin antibodies (TgAbs) concentration in dogs’ serum in order to assess thyroid functioning. The study was performed on 383 dogs. The animals were divided into two groups: group A (n = 308) consisted of dogs with hypothyroidism and group B (n = 75) consisted of dogs with euthyreosis. TgAbs was determined in both groups. The reaction to the TgAbs in group A was strongly positive in 32% of dogs, weakly positive in 33% of dogs, and negative in 35% of dogs. The TgAbs were observed in 32% of the dogs from group B, in which 8% of the animals had strongly positive reaction (++) and 24% - slightly positive (+). The correlation between the concentration of total and free fraction of the thyroxin and the level of the TgAbs were observed in group A. The tendency to positive reaction to the antibodies (++) in dogs with lower concentrations of total thyroxine and free thyroxine was observed. It was noted that the presence of the TgAbs was common in dogs with hypothyroidism. However, it could be also found in the animals with euthyreosis.