Background. It has been suggested that acetyl-carnitine may serve several potential functions in sperm, such as transporting medium- and long-chain fatty acids into the mitochondria for metabolism, maintaining a proper acetyl-CoA:free CoA ratio by buffering excess acetyl-CoA, serving as a storage medium for acetyl groups which may then be used as an energy source, and serving as an antioxidant. Objectives. To determine the effect of oral carnitine supplementation on the semen parameters: concentration, morphology and motility. Method. Observational study of 43 men with infertility and asthenozoospermia varying severity who receive acetyl-L-carnitine (1,000 mg per day) for a period of 3 months. The basic parameters of the ejaculate criteria were evaluated in accordance with WHO criteria. Results. There was no significant influence on sperm density and morphology, but Acetyl-L-carnitine supplementation demonstrated improvement in sperm motility. The amount of sperm category A was increased from 11±5% before treatment to 16±6% after treatment, p=0.004, for category B increase was from 13±7 to 19±12% before and after therapy, p=0.005, for category C increase was from 6±4% before treatment to 13±6 % after 3 months of treatment, p=0.004. Six spontaneous pregnancies occurred during follow up period (6 month), 4 pregnancies after in utero insemination and ten patients were referred to IVF clinics. Conclusion. Acetyl-L-carnitine supplementation (1,000 mg per day) demonstrated improvement in sperm motility, in men with idiopathic asthenozoospermia.