The purposes of this study were to (a) develop and validate instruments to assess elementary students' scientific creativity and science inquiry, (b) investigate the relationship between the two competencies, and (c) compare the two competencies among different grade level students. The scientific creativity test was composed of 7 open-ended items designed to assess divergent creativity and 2 open-ended items to assess convergent creativity. The science inquiry tests were composed of an open-ended inquiry (O-inquiry) test and a multiple-choice inquiry test (M-inquiry). The aforementioned instruments were verified with satisfactory validities and reliabilities in a pilot study. A total of 321 elementary students from grades 3, 4, 5 and 6 participated in the study to determine the performance differences detected by these instruments. It was found that both convergent and divergent creativity were significantly (p < .001) related with O-inquiry and M-inquiry. Analyses of variance revealed that there were significant grade-level main effects for scientific creativity and science inquiry. Post-hoc pair-wise comparisons revealed significant gaps between the 3rd graders' performances on scientific creativity and science inquiry and the performances of 4th, 5th, and 6th graders. Implications for curricular design and science teaching are discussed.