The study investigated the effects of a technology-integrated guided inquiry-based approach on pre-service mathematics teachers' conceptual understanding of geometry when compared to a guided inquiry approach and a traditional teacher-centered approach. A non-equivalent pretest-posttest control group quasi-experimental design was used. A three-stage sampling techniques was adopted. Two colleges were purposively selected and assigned to experimental and control groups through simple random sampling. A total of 116 pre-service primary mathematics teachers were assigned into three groups: experimental group 1 (n = 48), experimental group 2 (n = 38) and traditional group (n = 30). Pretest and posttest data were collected using a two-tiered test, and were analyzed with descriptive statistics, sample paired t-test and one-way ANOVA. Compared to the other two groups, pre-service mathematics teachers who received a technology-integrated guided inquiry-based approach showed a greater level of conceptual understanding. In accordance with the results, some recommendations were made for mathematics teacher educators.