Anti-inflammatory effects of three potassium salts of N,N-disubstituted 4-aminoazobenzenesulfonic acids were investigated and compared to that of acetylsalicylic acid (ASA) in rats with adjuvant arthritis (AA). Prophylactic oral administration of all compounds in a dose of 150 mg/kg ameliorated AA symptoms in animals. The most pronounced anti-inflammatory activity at the end of the experiment showed compound 1 containing imino group: it significantly suppressed joint swelling by 48.2% in female and by 44.2% in male rats with AA. The development of polyarthritis after the treatment with this compound was the lowest in female (20%) and male (40%) rats (in control--100% of animals with polyarthritis). All derivatives, and especially compound 1, also improved the systemic parameters of disease such as blood indices and internal organs' weight, and showed no toxicity on the main organs such as liver and spleen.