The effects of different doses of aqueous H. sabdariffa l. seed extract were examined on serum prolactin level in four groups of lactating female rats. Control, metoclopramide-treated and extract plus dopamine-treated groups consisted of five rats each (n=5). The extract-treated group was sub-divided into five sub-groups of five rats each and accordingly they were administered the extract in different five dose concentrations,one group for each dose. Female lactating rats were administered the extract (100, 200,400, 800 and 1600 mgkg-1 orally), metoclopramide (5 mgkg-1orally), extract (1600 mgkg-1)+ dopamine (5 μgkg-1 intraperitoneally), while control received normal saline (orally) from day 4-9 of lactation. The animals were then euthanized on the day 10 and serum prolactin levels were analyzed using prolactin kit. The serum prolactin level of the extract-treated rats showed a dose – dependent significant increase (P<0.01) when compared to control group. The extract plus dopamine-treated group did not show any change in serum prolactin level when compared to the control group. The LD50 of Hibiscus sabdariffa l. extract was found to be above 5000mgkg-1. Administration of the extract in a dose of 1g for four weeks did not show any significant changes in liver or renal functions of the treated rats. Keywords: H. sabdariffa, extract, acute study, lactation, prolactin, dopamine.