Crohn's disease and ulcerative colitis, better known as inflammatory bowel diseases, are chronic inflammatory diseases of the gastrointestinal tract. Healing of the mucosa and achieving deep remission is achieved by targeted therapy, however there are groups of patients who benefit exclusively from treatment with anti-inflammatory drugs from the group of 5-aminosalicylates; mesalazine and its prodrugs sulfasalazine, balsalazide and olsalazine. Folic acid deficiency has been observed in more than half of Crohn’s disease patients and more than a third of patients with ulcerative colitis. Its deficiency can lead to the development of megaloblastic anemia, and is associated with an increased prevalence of colorectal cancer, so in regular therapy, increased doses of folic acid of 1 to 5 mg per day are often prescribed. With the development of fixed-dose combinations, the potential risk of non-compliance with prescribed therapy is minimized, which is especially important in patients with chronic diseases where therapy consists of several drugs from different pharmacological groups. The development of fixed drug combinations is a complex process in which an important role is played by the examination of the physicochemical properties of each individual drug as well as their mixtures. In this paper, analytical methods are proposed to support the development of fixed combinations of 5-aminosalicylate and folic acid using various analytical techniques, such as thermal, spectroscopic and chromatographic, to test the physicochemical compatibility of 5-aminosalicylate and folic acid. Studies have shown that 5-aminosalicylates; mesalazine, sulfasalazine, balsalazide and olsalazine, are physicochemically compatible with folic acid, which opens the possibility for further testing required for the development of the proposed fixed combinations.