This study assessed the effects of Inquiry and Demonstration methods on Performance of Biology Students' in Secondary Schools in Federal Capital Territory, Abuja, Nigeria. The study was anchored on five objectives which include to: determine the performance of students taught Biology using Inquiry and those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja; investigate the performance of students taught Biology using demonstration and those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja; and to compare the performance of students taught Biology using inquiry and demonstration compared to those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja. Also, five research questions and five hypotheses were postulated in line with the stated objectives. Relevant literatures were reviewed on the key variables for this study. The study adopted quasi-experimental research design. The target population of the study comprised 23,422 SSII students consisting of 12,350 males and 11,072 females. A sample of 342 SSII students from six intact classes was purposively sampled from the entire 56 secondary schools in Abuja. The instrument used for data collection was a multiple-choice objective test titled "Biology Inquiry and Demonstration Performance Test (BIDPT)". The instrument was validated by the researcher's supervisors. The reliability of the instrument was pilot tested using a test/retest method. The reliability coefficient of the test/re-test scores was computed by means of Pearson Product Moment Correlation Coefficient (PPMCC) and a reliability value of 0.849 was obtained. The data was collected through the administration of pre-test and post-test. The bio-data of the respondents was analysed using descriptive statistics which involves frequencies and percentages while mean and standard deviation were used to answer the research questions. Independent t-test was used to test all the hypotheses at 0.05% level of significance. Findings of the study showed among others that students taught Biology using Inquiry method performed far better than those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja (.000 <0.005). The performance of students taught Biology using demonstration method was far better than those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja (.000 <0.005). Students taught Digestive System in Biology using inquiry method performed far better than those taught using conventional method in Secondary Schools in Federal Capital Territory, Abuja (.001 <0.005). The study concluded that, students tend to learn concepts in Biology as well as skills and how to solve problems using practical method and that Inquiry based learning require the student to do more than just report on a topic. Recommendations were made to include that teachers should use guided inquiry in teaching Biology more than unguided inquiry since the method has proved effective in enhancing students' academic performance in Biology. And that Ministry of Education and relevant academic and professional bodies like Science Teachers Association of Nigeria (STAN) and Teachers Registration Council of Nigeria (TRCN) should enlighten teachers on the use of inquiry and demonstration teaching methods through organized in-service trainings, workshops and seminars.