The aim of this pilot study was to determine whether nalbuphine shortens the duration of the active phase during the first stage of labour in pregnant women. Among 1,619 deliveries, we enrolled 302 pregnant women between March 2003 and August 2005. The case group received a nalbuphine injection (n = 57), while the remaining patients served as a control group (n = 245). The effects of nalbuphine on the length of labour were analysed using a survival analysis (log-rank test). The average duration of the initial active phase was 75 and 160 min for the case and control groups, respectively. The reduced duration of the active phase in the case group occurred regardless of oxytocin infusion (p < 0.01) and was without significant risks.