In the past several years there has been increasing interest in lightweight hydrogen absorbing alloys containing Mg and Ca. However, Mg and Ca that have low boiling points and high vapor pressure readily evaporate when they are synthesized by the melting method. It is difficult to get an alloy with a target composition because of the loss of Mg during the melting. We have developed a method that uses a helium gas mixture as an atmosphere during melting. Using this novel method, we successfully synthesized alloys with the composition that we expected.