The aim of the study was to investigate the effectiveness of mind mapping on Ethiopian secondary school students' English collocation learning. The study specifically tried to check the effectiveness of mind mapping on adjective-preposition and verb-noun combination collocations. A sample of 110 grade 12 students who were learning in two sections at Majete General Secondary School, North Shoa Zone, Ethiopia, participated in the study. One of the two sections was randomly assigned to an experimental group, while the other one was labeled as a control group. A pre-test and two post-tests were used as data-gathering instruments. The data were analyzed by using mean scores, paired samples, and independent sample t-tests. The results revealed that although the two sections had no significant difference in their pre-test results, in the immediate and delayed post-tests, the score of adjective-preposition & verb-noun collocations of the experimental group students was significantly higher than the score of the control group students who learnt those collocations without mind map. Based on this, it could be concluded that using mind map was an effective strategy to improve EFL high-school students' collocations learning. Accordingly, it is recommended that EFL teachers and students should use mind-map during their collocations lessons.