BACKGROUND A number of antimalarial compounds and herbs have been reported to possess antifertility actions. Amodiaquine (AQ) belongs to the same class of drugs as chloroquine. Chloroquine has been reported to disrupt the oestrus cycle, block ovulation and consequently reduce fertility. OBJECTIVE This study was carried out to investigate the effect of the administration of amodiaquine hydrochloride (AQ.HCl) on fertility in the adult cyclic Sprague-Dawley rats. METHODS Thirty cycling female albino rats of Sprague-Dawley strain weighing 120 g were used in this experiment. They were divided into six experimental groups. Groups 1A, 1B and 1C- received peroral (p.o.) 6 mg/kg bw of AQ.HCl, 12 mg/kg bw of AQ.HCl and distilled water for 28 days respectively to determine the effect of AQ.HCl on the oestrous cycle. Groups 2A, 2B and 2C- received a single dose p.o. of 6 mg/kg bw of AQ.HCl, 12 mg/kg bw of AQ.HCl and distilled water at 9 a.m. on proestrus respectively to determine the effect of AQ.HCl on ovulation and the serum concentrations of follicle stimulating hormone (FSH), luteinizing hormone (LH) and prolatin (PRL). RESULTS AQ.HCl disrupted the oestrous cycle by producing a significant (p < 0.05) increase in the diestrus phase and a reduction in the other phases when compared with the control. A significant reduction (p < 0.05) in the number of ova shed on estrus was observed however, there was no significant difference in the serum concentrations of FSH, LH and PRL when compared with the control. CONCLUSION Oral administration of AQ.HCl distrupts the oestrous cycle and ovulation by increasing the frequency of the diestrus phase and reducing the number of ova released at ovulation respectively. These events may negatively affect fertility in females of reproductive age.