<p>Background: The hormones of hypothalamo-pituitary-gonadal (HPG) axis have facilitative effects on reproductive behavior in mammals. Ghrelin as a starvation hormone has an inhibitory effect on HPG axis&rsquo; function. Hence, it is postulated that ghrelin may reduce the sexual behavior through inhibiting of HPG axis. The aim of this study was to examine the effects of ghrelin and its antagonist, [D-Lys³]-GHRP-6, on sexual behavior and LH beta-subunit gene expression in male rats.<br /> Methods: In this experimental study, 128 male Wistar rats were divided into two groups. Each group was further subdivided into eight subgroups (n=8 rats/subgroup) including the animals that received saline, ghrelin (2, 4 or 8 <em>nmol</em>), [D-Lys³]-GHRP-6 (5 or 10 <em>nmol</em>) or co-administration of ghrelin (4<em> nmol</em>) and [D-Lys³]-GHRP-6 (5 or 10 <em>nmol</em>) through the stereotaxically implanted cannula into the third cerebral ventricle. The sexual behavior of male rats encountering with females and the hypophyseal LH beta-subunit gene expression were evaluated at two different groups. Data were analyzed by ANOVA and p&lt;0.05 was considered statistically significant.<br /> Results: Ghrelin injection (4 and 8 <em>nmol</em>) significantly (p&lt;0.01) increased the latencies to the first mount, intromission and ejaculation as well as the post-ejaculatory interval. Also, 4 and 8 <em>nmol</em> ghrelin significantly (p&lt;0.05) increased the number of mount and decreased the number of ejaculation. In co-administrated groups, [D-Lys³]-GHRP-6 antagonized the effects of ghrelin. Ghrelin injection (4 and 8 <em>nmol</em>) reduced the LH beta-subunit gene expression while pretreatment with [D-Lys³]-GHRP-6 improved the gene expression.<br /> Conclusion: Ghrelin decreased the sexual behavior and LH beta-subunit gene expression in male rats, whereas [D-Lys³]-GHRP-6 antagonizes these effects.</p>