This study aims to analyze the implementation of discovery strategies in integrated thematic learning of IPA subject matter of light traits in fourth grade MI Ma'arif Gondosuli Muntilan academic year 2018/2019. This study also explains the effectiveness of discovery strategies in integrated thematic learning of IPA subject matter of light traits in the fourth grade of MI Ma'arif Gondosuli Muntilan academic year 2018/2019. Research uses qualitative research using observation techniques, collection of data from the field, and documentation. The results of the study are as follows: First, the discovery strategy begins with a little explanation of the material then continues the students to do experiments which include the nature of light can propagate particles, can penetrate clear objects, light can be reflected and can be refracted. This activity begins with students observing the experiment, then asking, gathering information, reasoning and communicating orally and in writing in the form of reports. Second, the effectiveness of this strategy is known from the enthusiasm of students in doing group work, dividing the tools that will be taken when conducting the experiment. In addition, this strategy can improve the creativity of students and teachers in conducting learning in order to foster a sense of enthusiasm in learning. Then in cognitive values, after the post-test shows the value that exceeds the KKM except for two students, where this can be an indicator of the effectiveness of the strategy.