The synthesis of a group of thiazolidine derivatives with pyrazolone-5 substituent is described. The structure of the new compounds is supported by 1H- and 13C-NMR spectra. Group of compounds was tested in vivo for their antiinflammatory activity. The obtained results gave the opportunity to separate the perspective groups of potential NSAIDs, which have got greater antiinflammatory activity than the best standard drugs.