This study examined the acquisition of Korean stop sounds /t/(), /t/() and /th/() by Chinese learners of Korean using ERPfocusing on the role of L2 proficiency. A total of 28 learners (16 advanced and 11 intermediate) and 18 native controlsparticipated in the experiment with four conditions: (i) standard /ta/ vs. deviant /tha/, (ii) standard /ta/ vs. deviant /t/, (iii)standard /tha/ vs. deviant /ta/, and (iv) standard /ta/ vs. deviant /ta/. The results of the AX discrimination task found nosignificant differences between groups showing high accuracy rates from 73% to 84%. However, their brain responseswere different: P3 was found only for the intermediate group in condition (iii) although MMN was elicited in both groupsin the other three conditions. The results indicate that learners sensitivity to the differences of stop sounds develops astheir general proficiency improves. Still, their sensitivity is weaker than native speakers.