This study investigated the effects of two vocabulary instructional approaches on Chinese EFL primary school students (n = 31) to vocabulary learning, extended and incidental instructions, with using a between-subject design. Student's general intelligence and initial English ability were entered as covariates. The extended instruction featured multiple encounters to vocabulary, providing opportunities to apply as well as encouraging active and deep processing. The incidental instruction featured natural exposure to the words and learning vocabulary through readings. The instructional effects on student's vocabulary knowledge were assessed by three measures: target word mastery, expressive definition as well as word association. Extended instruction showed an advantage in building up vocabulary breadth in students compared to incidental instruction. Both instructions seemed inefficient on enhancing depth of vocabulary knowledge. Implications of present findings are discussed and directions about future research are suggested. All rights reserved.