This research was aimed to analyze the effect of interaction between guided inquiry learning and cognitive style on students' science learning achievement. This study was a quasi-experiment with a 2×2 factorial design. The study was done with the fifth grade students in Singaraja City. The sample was selected using multi stage random sampling and 4 elementary schools were selected for the experimental group (n=132) and another 4 for the control group (n = 107). The experimental group used guided inquiry learning and the control group used conventional teaching model. The study used science learning achievement test and MFFT [Matching Familiar Figures Test] cognitive style test as the instruments for collecting the data. The result of hypothesis testing showed that: (1) there is a significant difference in science learning achievement between those who learned with guided inquiry learning model and those who learned with conventional teaching; and (2) there is a significant effect of interaction between guided inquiry learning model and cognitive style on students' science learning achievement. Guided inquiry learning is more optimal in increasing students' learning achievement if it is implemented to students with reflective cognitive style than to those with impulsive cognitive style.