There has been plenty of observational evidence displaying that L2 English learners whose L1 do not have article systems undergo persistent difficulties. It is known that functional categories of grammar are especially difficult for L2 learners, and the Korean language does not have a functional equivalent to English articles. The current study aims to investigate article usage patterns by L1 Korean L2 English learners by employing a large English interlanguage corpus data; ICNALE written corpus data. Particularly, the current study focuses on the analysis of a specific NP, "part-time jobs". The current research claims that by narrowing down the scope of analysis to a particular NP, one can expect more reliable and meaningful interpretation from L2 learners' authentic language production, which can ultimately lead to more effective language instruction and better outcomes for second language learners. The current study seeks to describe patterns of L2 English articles across different proficiency levels. According to the results, it was found that learners' article usage patterns appeared to be more similar to that of the native speaker in the group with higher English proficiency. One of the interesting findings was the frequent use of bare nominals even in the most advanced learners. Based on the corpus analysis, the current study provides the pedagogical implication that teaching structural differences between learners' L1 and L2 is very important and article instruction should be emphasized in L2 classrooms in EFL settings.