Many studies showed that organization of study materials has a strong effect on learning performance (Kornell & Bjork, 2008). The current study compared category learning performance through blocked and interleaved learning conditions, using verbal (Experiment 1) and pictorial (Experiment 2) materials. Participants were assigned to one of three conditions at encoding phase: blocked, interleaved, and semi-interleaved learning conditions. In blocked learning, participants studied four exemplars of the same category within the same trial, and categories were blocked across trials. In interleaved learning, participants studied one exemplar from four different categories within the same trial, and categories were interleaved across trials. In semi-interleaved learning, participants studied four exemplars of the same category within the trial, but categories were interleaved across trials. At testing phase, participants were tested on old and novel exemplars of the categories that they studied and were asked to identify the category of each exemplar. Lastly, they were tested on explicit understanding of categories. Both Experiment 1 and 2 revealed that participants produced the highest learning performance in the semi- interleaved learning condition. Learning similarities within the same trial and learning differences across trials might lead to the most optimal learning strategy for category learning, regardless of the type of stimuli used.