Background: The aim of the work is to determine the effectiveness of deep tissue massage therapy on mobility and pain of the thoracic spine. Material and methods: The study involved 18 women and men aged 46–63 years doing office work. Functional diagnostics was performed prior to the therapy (study I), after the procedure (study II) and after 30 days (study III). The Otta test for flexion and extension of the spine, pectoralis major muscles length test, chest circumference measurement, and NRS were used. In the statistical analysis mean and standard deviations were determined and the following tests were used: Mann-Whitney U, Spearman's Rank Correlation, Pearson’s Chi2, Shapiro-Wilk, Friedman, and ANOVA. Statistical significance of the differences was estimated at p <0.05. Results: The results of the diagnostic tests obtained in men and women did not differ statistically, which allowed for further consideration as one group of patients. The results of mean differences in the spine extension between study I and II (D=1.06, p=0.001) and I and III (D=0.83, p=0.001) indicate improved spine mobility. The D=-0.22, p=0.041 result between the II and III test indicates a deterioration in the spinal extension. A similar tendency was observed in the results of the pectoralis major muscles length study. The results of mean differences in the chest circumference between study I and II (D=-1.61, p=0.001) and I and III (D=-1.33, p=0.001) indicate an increase in the chest circumference. The mobility of the chest after 30 days did not change (D=0.28). The mean differences in the NRS between the study I and II (D=5.22, p=0.001) and I and III (D=4.22, p=0.001) show a reduction in pain. The D=-1.0, p=0.001 score between tests II and III means that the improvement was not at the same level as immediately after the therapy. Conclusions: Deep tissue massage is an effective method in the treatment of pain located in the thoracic spine. It improves the mobility of the spine and the chest, and the length of pectoralis major muscles in people doing work in a sitting position.