The purpose of this research is to study the effects of using portfolio assessment on the science inquiry ability and to find out the differences depending on learning competence levels in elementary schools. To do this, the detailed contents of the study were as follows; First, are there any meaningful differences of science inquiry ability between the group assessed by portfolio and the conventional group in science classes of elementary schools? Second, based on learning competence levels, are there any differences of the application effects on science inquiry ability? For this study, 6th grade classes at an elementary school in Pusan for 6 weeks, were selected as a control group(30 children) which were chosen as the highest equality to the experimental group by a previous test. Through reviewing the previous researches, the most proper model of portfolio assessment was proposed and applied which was argued by Hill & Ruptic(1994), Suk-woo Kim(2000), Eun-kyung Sung(1999) and Han-moo Cho(1997). The test of science inquiry ability was implemented by the reconstructed \'test of science skill‘(Kwon & Kim(1994)). And then the results were verified by the t-test. Therefore, the results of this study are summarized as follows. First, there is a meaningful difference statistically(p＜.001) in the portfolio assessed group from the conventional group, as well as, the portfolio assessment effects on the promotion of science inquiry ability in elementary school students. Second, portfolio assessment had a significant effect on the abilities of reviewing, classifying, anticipating, material analyzing and generalizing which are subclasses of science inquiry ability(p＜.05). But it did not make a difference statistically in calculating ability and value control ability(p＜.05).control ability(p＜.05). Third, depending on learning competence level, it also showed a meaningful difference on both high and low level students(p＜.05). Therefore the portfolio assessment gave an effect on every students\' science inquiry ability regardless of their learning competence level. Fourth, depending on the learning competence level, portfolio assessment also had an important effect on the subclasses of science inquiry ability on both high and low level students(p＜.05). Therefore, the portfolio assessment showed effects on the subclasses of science inquiry ability for every student regardless of their learning competence level. And it did not make a difference statistically in anticipating the ability of both high and low level students, however the average arose. In conclusion, the application of portfolio evaluation as an instruction and an evaluation process would be very important to promote science inquiry ability. And this also would effect on high and low level students depending on their learning competence level.