Abstract: Objective: To evaluate the effects of priming on the time of rocuronium and vecuronium.Methods: 20, ASA grade Ⅰ Ⅱ patients undergoing elective plastic surgery were randomly allocated to four groups. Three minutes after a bolus of normal saline 1 ml, rocuronium 0 6 mg/kg and vecuronium 0 1 mg/kg were administered in group Ⅰ and group Ⅲ, respectively. Group Ⅱ and Ⅳ received a priming dose of rocuronium 0 06 and vecuronium 0 01 mg/kg followed by a intubating dose of rocuronium 0 54 mg/kg and vecuronium 0 09 mg/kg. The priming interval was 3 min. The onset time was recorded and analyzed.Results: Onset time in group Ⅰ and group Ⅲ were （1.4±0. 3）and （4.8±0.2）min, respectively and the onset time of group I was obviously shorter than group Ⅲ （ P ＜0.01）。There was no different between group Ⅱ and group Ⅰ, （1.3±0. 2）and （1.4±0.3）min. In group Ⅳ and group Ⅲ, the onset time were （1.5±0.4） and （4.8±0.2）min, respectively. Onset time in group Ⅳ was significantly shorter than group Ⅲ （ P ＜0.01）. Conclusion: The onset time of rocuronium was significantly shorter than which of vecuronium. Rocuronium was ineffective in priming itself. Vecuronium was effctively in priming itself.