The aim of the study was to develop an analytical method adequate to determine the tiamulin in plasma after administration in therapeutic values, calculation of the pharmacokinetic parameters of tiamulin in broiler chickens and the evaluation of the bioequivalence of two veterinary formulations. In order to determine the tiamulin in investigated material the HPLC technique with UV-VIS detection was used. After oral administration of tiamulin as Tiamulina 10% and Tiamutin 12.5% the following pharmacokinetic parameters were calculated: AUC, Cmax, tmax, t₀,₅, Vd, kel and MRT. For the pharmacokinetics analysis a PK Solution 2.0 computer program was used. Results of the study indicate quite a rapid absorption of tiamulin from the gastrointestinal tract as well as its quick elimination from plasma. The high value of the volume of distribution indicates the peripheral compartment is a target compartment for tiamulin. Results of statistical analysis including pairs of pharmacokinetic parameters like tmax, Cmax, AUC and the evaluation of percentage differences among them, allows the authors to conclude that formulations used in the study are bioequivalent.