ECOSOC comprises 54 UN member countries.
Croatia was already a member of the body in 2000-02, chairing it in 2002.
The new membership is an acknowledgement of Croatia's international position and reputation as well as an opportunity to contribute to the promotion and implementation of economic and social policies important to the UN, the ministry said.
Croatia was elected as a member on Thursday alongside Albania, Benin, Bolivia, Canada, Colombia, Haiti, Kuwait, Kyrgyzstan, Mauritius, Nepal, the Netherlands, San Marino, Sudan, Tunisia, Turkmenistan and the United States.
Croatia's term begins on 1 January 2013 and ends on 31 December 2015.