Abstract: The aim of this study was to compare the efficacy of atropine and hyoscine-N-butyl bromide in reducing the pain and time length of the first stage of labour. In a single blind randomized clinical trial, 120 term pregnancies were enrolled from July 2009 to March 2011. A parallel design was used to randomly assign subjects into two equal groups including 60 participants in each group. Hyoscine-N-butylbromide was administered 40 mg intravenously in the first group and intravenous atropine was given in second group at a dose of 0.5 mg. The participants of the two trial arms were similar according to the distribution of background variables. The pain trend through the study follow up was found to be different between groups (p<0.05). Mean length of the first stage of labor was 218.5 min (SD: 81.4) in hyoscine versus 339 min (SD: 83.3) in atropine group (p<0.001). Mean 1st and 5th min APGAR score was similar in both groups. Drug side effects were less frequent in hyoscine group observed in 13 cases compared to atropine group observed in 56 cases (p<0.001). Hyoscine appeared to be preferable to atropine specially in reducing the length of first stage of pregnancy.