Abstract: The present invention relates to an improved process for the preparation of thiourea. The object of the present invention is to provide an improved process for the preparation of Thiourea using Calcium Cyanamide, carbon dioxide and hydrogen sulphide. The process of the present invention comprises passing a mixture of Carbon dioxide ad hydrogen sulphide into a slurry formed by addition of major part of calcium cyanamide charge into water using constant stirring, maintaining alkaline pH at a temperature ranging between ambient to 80° C., stopping the addition of hydrogen sulphide, continuing the slow passing of carbon dioxide and addition of remaining part of calcium cyanamide charge and retaining the reaction mass to complete the secondary reactions to form the product for a period ranging from 2-5 hours and continuing passing of carbon dioxide at an increased rate for effecting decomposition of Ca(SH)2 for a period of 1.