The purpose of this study is the development of the observation Assessment criteria that is used to assess manipulative skills in elementary science. The procedures of developing observation Assessment criteria are as follows. First, we investigated the actual condition about science process skills assessment with the questionnaire. Second, we selected 7 experimental apparatus through the analysis of the science textbooks. The selected experimental apparatus are dropper, alcohol lamp, thermometer, test tube, filtering device, table balance, graduated cylinder. Third, the observation Assessment criteria are developed through the analysis of the related experimental textbooks, the demonstrations, and the questionnaire. Forth, the validity is verified by science education specialists and graduate students who major in science education. Fifth, the first inter-rater agreement is investigated in the result of the field with observation criteria of which the validity was verified. The second inter-rater agreement is investigated through the revision and the addition of the criteria with the low agreement. In result, the inter-rater agreement ranged from 0.86 to 0.98. One of the major problems in observation assessment is the rater`s subjective viewpoint. So, this research shows a more specified scale and criteria for the assessment. This suggests that the observation Assessment criteria developed in the study satisfies the high reliability and validity requirements. Considering the results, this criteria can be used effectively for assessing manipulative skills of elementary school students.