This study explored the effects of collaborative writing instruction on undergraduate nursing students' writing performance and self-efficacy beliefs within an online learning system. A single-group experimental study utilized two instruments, the NCEEC (National College Entrance Examination Center) writing grading criteria (the SRCT) and a modified writing self-efficacy questionnaire (the WSQ), was conducted. The intervention was applied in the context of a four-month freshmen semester at the beginning of a two-year vocational education program conducted in fall 2010. Two hundred and nine learners were recruited through convenience sampling from four classes at a nursing vocational university in southwestern Taiwan. Quantitative data were analyzed using descriptive statistics, repeated measures MANOVA, explorative factor analysis (EFA), and structural equation modeling (SEM). The results showed that this instructional method effectively improved the learners' writing performances and also influenced the latent structures of the learners' self-efficacy from theoretical constructs toward pedagogical meanings, with the learners' writing self-efficacy beliefs being altered by the instruction and becoming consistent with the assessment criteria. In addition, both the learners' pre- and post-test self-efficacy levels had significant causal relationships with their individual learning progressions. These correlations between self-efficacy and writing performance suggest further teaching implications.