Provided are a composition containing L-carnitine and at least one β-hydroxybutyrate compound; said β-hydroxybutyrate compound contains β-hydroxybutyrate and a β-hydroxybutyrate precursor or a combination thereof; preferably, the L-carnitine and β-hydroxybutyrate in said composition are present in the form of an intramolecular salt. Also provided is a method for preparing L-carnitine-β-hydroxybutyrate. The composition has weight-loss and ketogenic effectiveness.