Based on Vygotskian sociocultural theory, this study aims to investigate the longitudinal changes in English as a second language (ESL) learning, especially on motivation and learner beliefs for two recent Korean immigrants to Toronto. For 10 months, the researcher interviewed the two participants who shared similarities in age, previous work experiences, and perceived socio-economic status. Their comments were tape-recorded, transcribed, and analyzed by using NVivo, a qualitative data analysis software program. The findings indicate that Korean immigrants' ESL learning motivation was comprised of six constructs: job motivation, communicative need, heuristic motivation, context-specific motivation, self-satisfactory motivation, and demotivation/amotivation. Despite the two participants' external similarities, their monthly changes in ESL learning motivation showed drastic differences. An L2 learner belief of the positive relation between English proficiency and increased job opportunity was identified as a major explanatory factor for this difference between the two participants. This study suggests that L2 learner's beliefs may function as mediational tools from the perspective of sociocultural theory, with the learner's belief influencing job motivation.