The purpose of this study was to determine the effect of Blended Project-Based Learning (BPjBL) with the STEM approach to spatial thinking skill and geography skill and student's attitudes in implementing the learning. The research design used quasi-experimental research and independent t-test and paired t-test as data analysis. The selection of population was used random sampling techniques to second-year students of National Senior High School 1. Population in this study was the social science class at SMA Negeri 1 Kepanjen Malang, Indonesia. The students were divided into two groups, experimental group from social class 1, which used the BPjBL and control group from social class 3, which used the conventional method. The results showed that there was a significant influence of BPjBL with STEM approach to spatial thinking skill and geography skill. The changes in students' attitudes also shown significantly towards spatial thinking skill and geography skill. This research proved that the application of project-based learning could develop spatial thinking skill and geography skill as 21st-century learning objectives.