The purposes of this study are to understand the influence of L1 on learning Korean negation and a developmental sequence of Korean negation forms through examining English and Japanese learners of Korean. In particular, we aim to investigate whether linguistic distance between L1 and L2 affects learning Korean negation. Forty English and twenty Japanese students who were learning Korean in colleges participated in the written production test. As a control group, forty Korean native speakers took the written test. We observed that the English and the Japanese groups produced less number of long form negation sentences than the Korean adult group did. The English group showed a developmental pattern to advance from short to long forms, while the Japanese group demonstrated the opposite tendency. These results suggested that an influence of L1 negation structure on L2 learning coexisted with that of a general developmental sequence. The pedagogical implications of the findings are two-fold:1) the findings would provide practical suggestions for instructing Korean negation forms in multilingual classrooms and 2) the findings would help researchers and language teachers understand the learning patterns of Korean by L2 learners.