The purpose of this was to investigate the effect of guided inquiry teaching method on students’ academic achievement in the concepts of flowering plants: grade seven students at Dilchibo Primary School. This research had three research questions, and two null-hypotheses. The target population of this study was grade seven Dilchibo Primary School students. The research design was quasi- experimental pre-posttest design. The sample size of this study was grade seven one group controls and other group experimental; the total sample 105 students were selected by simple random sampling techniques. The study employed both qualitative and quantitative method. To answer the research question the data collection instrument of the study was biology achievement test and classroom observation. The result of quantitative data showed that, experimental group students post test result was better academic achievement to compare control group students’ and also the result of qualitative data showed that the experimental group students the post assessment result was better conceptual understand, that implies the students’ academic achievement improved than lecture method after the series of learning experimental group students’ better conceptual understanding in flowering plants to compare control group students. It implied that guiding inquiry teaching method was an effective teaching method to develop students’ conceptual understanding and academic achievement. Therefore, in order to develop students’ academic achievement in flowering plant biology teachers should apply an innovative method like guiding inquiry teaching method.