The problem of the present invention is to prove a medicament for decreasing body weigh, a medicament for decreasing visceral fat, a medicament for decreasing triglyceride in the liver, and a method for screening a medicament for ameliorating obesity and fatty liver. The problem is solved by a method comprising measuring an activity of a candidate material for inhibiting a sphingomyelin synthetase wherein if the candidate material has an activity for inhibiting a sphingomyelin synthetase, the candidate material is judged to have at least one function selected from the consisting of an anti-obesity drug, a drug for decreasing visceral fat, a drug for treating fatty liver and an agent for increasing adiponectin expression.
