This study is to investigate the Impact of Inquiry-Based Instruction on Self-efficacy and Understanding of Nature of Science among NCE Biology Students. There are four research questions and four null hypotheses. The research design for the study was quasi experimental which adopted the pretest-posttest experimental control groups design. The population for the study comprises of all the NCE1biology students of three State Colleges of Education in Kwara State with the population of two thousand two hundred and seven. The sample consisted of ninety NCE1 biology students that were drawn from two colleges of education, forty five from each college, from the two colleges of education from the population of one thousand four hundred and sixty seven using table of randomization. The students were randomly assigned to experimental and control groups. The experimental groups were taught cell biology using inquiry-based instruction while the control groups were taught cell biology using lecture method. A pre-test using Nature of Science Understanding Test (NOSUT) and Nature of Science Self-efficacy Questionnaire (NOSSEQ) was administered to the Inquiry-based instruction group and Lecture method group respectively to determine their entry level in understanding of nature of science before treatment. NOSUT and NOSSEQ were administered as post-test to both the Inquiry and Lecture method groups to find out the impact of the treatment. The two instruments used for data collection, (NOSUT & NOSSEQ) have the reliability of 0.96 & 0.79 respectively. The data obtain was used in analyzing the research question and the hypotheses stated was subjected to test using t-test statistics at 0.05 level of significance, while Pearson Product Moment Correlation Coefficient (PPMC) was used in determining the relationship between the groups. From the result obtained the hypothesis one, two and four were rejected while hypothesis three was retained. The summary of the findings revealed that understanding of nature of science and student?s self-efficacy was enhanced through exposure to inquiry instruction. Base on the findings: The structured inquiry-based instruction is very effective in enhancing self-efficacy and understanding of nature of science by NCE students. Lecturers should employ structured inquiry-based instruction in teaching cell biology concepts so as to improve students? self-efficacy and understanding of nature of science in cell biology