The present study aimed to investigate the effects of blended learning instruction on vocabulary knowledge of Thai primary school students and students' perceptions toward learning vocabulary through blended learning instruction. A mixed-methods approach was used. Quantitatively, a single group pretest-posttest design was used to measure students' vocabulary knowledge after ten weeks of vocabulary lessons via blended learning instruction. The qualitative method focused on students' perceptions toward blended learning instruction. There were a total of eight student participants at a small school in Kosumphisai, Maha Sarakham province. Three students were in fifth grade and five students in sixth grade. Two research instruments were used in this study: a pre-and-post-test and an in-depth interview. The quantitative results revealed that the post-test score was higher than the pretest score. The blended learning instruction can improve the students' vocabulary knowledge. The qualitative results showed that students had positive attitudes toward blended learning instruction on vocabulary teaching.