The invention relates to novel cosmetic uses of phytosphingosine or of one of its cosmetically acceptable salts, particularly its hydrochloride, as a slimming agent and/or as an active agent which stimulates the synthesis of leptin by adipocytes, for preparing a cosmetic composition intended for reducing subcutaneous excess fat.The invention also relates to a method of cosmetic treatment intended for obtaining a slimming effect on the human body according to which a cosmetic composition containing phytosphingosine or one of its cosmetically acceptable salts, particularly its hydrochloride, is applied on the parts of the body to be treated.The invention also relates to novel cosmetic compositions containing phytosphingosine or one of its cosmetically acceptable salts, particularly its hydrochloride, in combination with a lipolytic agent selected from the group consisting of cAMP and its derivatives, adenylate cyclase enzyme activating agents and phosphodiesterase enzyme inhibiting agents.