The affordance of mobile-based learning, including supporting a more personalized, authentic, situated learning are obvious. Research also revealed that mobile learning had positive effects on Second Language (L2) learning. However, individual differences on learning styles and prior knowledge could significantly affect the learning outcomes. This study aimed to investigate the effects of learning styles (field independence/dependence, FI/FD) and prior English proficiency (high/low) in a mobile augmented reality (AR) facilitated English vocabulary learning. Target subjects were elementary school children learning English as L2 and learning objective was set to memorize/understanding a set of ten English vocabulary. An experiment was done with self-developed AR-facilitated instruction. The results indicated that that FD learners benefitted significantly better from the mobile AR instruction on learning outcome; there was a marginal significant difference between high and low English proficiency learners on learning outcome; and neither learning styles nor prior English proficiency affected learning motivation. These findings indicated that individual differences should be considered while mobile AR L2 vocabulary instruction was applied.