【Objective】A study on the diminazene-protein binding rate in swine was carried out in this experiment for further clinical application efficiency and safety.【Method】The plasma samples were pretreated to separate free drug by ultrafiltration. A high performance liquid chromatographic-UV (HPLC-UV) method was used to measure the amount of free diminazene in plasma. Then the drug-protein binding rate was accounted. Six swine were administrated intramuscularly at a dosages of 7 and 14 mg/kg. The plasma samples were collected and the protein binding rates in vivo were determination at 3, 5, 15, 60 min.【Result and conclusion】Diminazene-protein binding rate tested in vitro was within the range of 74.68%-95.90%. Although the drug-protein binding rate in vivo was within the range of 84.11%-89.69%（7 mg/kg, i.m.）, and 82.96%-88.65%（14 mg/kg, i.m.） after administration, and saturation phenomenon emerged as dosage increased. These factors should be considered in clinical regimens designing.