In the past, students' science learning self-efficacy (SLSE) was usually measured by questionnaires that consisted of only a single scale, which might be insufficient to fully understand their SLSE. In this study, a multi-dimensional instrument, the SLSE instrument, was developed and validated to assess students' SLSE based on the previous literature. Besides, the interrelations between students' approaches to learning science and SLSE were explored. A total of 311 Taiwanese eighth graders were invited to respond to the SLSE instrument and the Approaches to Learning Science (ALS) questionnaire. After ensuring several types of validity (e.g. construct validity and criterion-related validity) and the reliability of the SLSE questionnaire, the results suggested that the SLSE instrument should have satisfactory validity and reliability to measure Taiwanese eighth graders' SLSE in terms of 5 dimensions: Conceptual Understanding, Higher-Order Cognitive Skills, Practical Work, Everyday Application, and Science Communication. Moreover, through Pearson correlation analyses, the results revealed that the Taiwanese eighth graders who perceived themselves as having a deep motive, along with the orientation of surface motive, tended to report higher SLSE. Also, those students who reported adopting deep strategies to learn science were more likely to possess higher SLSE. The regression results indicated that, overall, the students' deep strategies and deep motive were strong predictors of their SLSE, particularly for the Higher-Order Thinking Skills SLSE. Yet, the Practical Work SLSE could only be predicted by the Deep Strategy dimension of ALS.