The evaluation of the effective rainfall is important in the design and operation of irrigation systems. But the definition of the effective rainfall and the method for the estimating effective rainfall is various for each purpose. In this paper, the effective rainfall was defined as amount of rainfall which is remained in the effective soil depth that can be use to consumptive use of crop during growing season. The soil moisture was measured by Neutron prob for the effective rainfall estimation, and the experiment was conducted for mulched and non-mulched condition of lysimeter during growing season. B\' the result of analysis and the former definition, the effective rainfall was estimated to be 37.2% for the mulched lysimeter and 40.7% for the non-mulched lysimeter.