Introduction: Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are the most common inflammatory, chronic, progressive rheumatic diseases. They primarily affect the musculoskeletal system and cause damages that leads to a significantly reduced quality of life. Biological disease modifying antirheumatic drugs reduce inflammatory and immune reactions, lead to a reduction in symptoms and an improvement in the quality of life in patients with RA and AS. Objective: The aim of this study was to assess the quality of life in patients with RA and AS before and after treatment with biologic therapy. Methods: A retrospective observational study that covered the time period from 2016. to 2020. and included 100 patients with a confirmed diagnosis of RA and AS. The results of measuring instruments, predictors of quality of life, VAS pain, VAS-GH, HAQ-DI, FACIT-F were collected from the existing medical documentation of the Hospital Information System of the Clinic for Rheumatic Diseases and Rehabilitation, KBC Zagreb, immediately before the application of biological therapy and nine months after application of the same. Results: Statistically significant changes were observed between the two measurements within the observed period in patients with RA and AS. Conclusion: The application of biological therapy in patients with RA and AS who do not respond adequately to conventional therapy, has proven to be an important pharmacological strategy in improving quality of life.