HSK21542 injection is a new peripheral kappa opioid receptor (KOR) agonist. To evaluate its safety, tolerability, pharmacokinetics and pharmacodynamics, this study was conducted in healthy volunteers, consisting of two parts: a single ascending dose (0.2-3.375 μg/kg, 15-min infusion) and different infusion durations (0.2 and 1 μg/kg, 2- or 15-min infusion). The area under the plasma concentration-time curve (AUC) and peak concentration (C) of HSK21542 were dose-linear among 0.2-3.375 μg/kg. After intravenous injection, HSK21542 was rapidly eliminated with a half-life (t) of 1.5 h, and the majority (48.02%) of the dose was excreted unchanged in urine. Pharmacodynamic results showed that HSK21542 increased prolactin release and reached a peak at 1-2 h after administration but had no significant effect on vasopressin levels. There was a brief increase in urine volume within the initial 2 h after administration. HSK21542 was well tolerated; most of the adverse effects (AEs) in the trial group were grade 1, and only 2 cases (4.0%) were grade 2. The main AE was paresthesia, which appeared in 42% (21/50) in the trial group. No serious adverse event (SAE) was observed. No subject withdrew early due to AEs. These results suggest that HSK21542 may be a potential treatment for pain and pruritic conditions.