On March 21, in order to determine the effect of melatonin and plane of nutrition on reproductive parameters of anoestrous Rasa Aragonesa ewes, half of the animals of two groups fed 1.2 (high group, A, n = 20) or 0.5 (low group, B, n = 22) times the maintenance requirements were implanted (treated group, M, n = 21) or not (control group, C, n = 21) with a subcutaneous implant of melatonin. Thus, the experiment was designed as a 2 x 2 factorial (AM, n = 10; BM, n = 11; AC, n = 10; BC, n = 11). Rams were introduced in the flock on May 5, 45 days after implantations. There were no significant differences either for percentage of oestrous ewes or fertility rate, although the effect of melatonin on ovulation rate was significant (P < 0.01), with a trend for the effect of plane of nutrition (P < 0.1) (AM: 1.89 ± 0.26; AC: 1.33 ± 0.17; BM: 1.50 ± 0.17; BC: 1.00 ± 0.00 corpora lutea). Melatonin‑treated ewes had a higher litter size (M: 1.50 ± 0.14: C: 1.09 ± 0.09; P < 0.05), independently of plane of intake (A: 1.33 ± 0.14; B: 1.31 ± 0.13), giving rise to 75% extra lambs born per treated ewe in comparison with control animals (M: 1.00 ± 0.18; C: 0.57 ± 0.13; P < 0.1). In conclusion, the improved lamb production presented by melatonin‑treated animals can be mediated, in part, by an improvement of ovulation rate, especially in underfed ewes.