This study quantitatively investigates foreign learners" acquisition of double particles in Korean. Some of the particles in Korean are jointly used with other particles and some are not, and the sequence of the particles determines the grammaticality of the double particles. Chinese and Japanese learners of Korean participated in the experiment in which they were asked to judge the grammaticality of a combination of a noun and double particles. The participants" judgment of the grammaticality of the double particles and their reaction time for the judgment were analyzed. The results of the study revealed that Japanese learners whose native language has a particle system similar to that of Korean performed better in the grammaticality judgment than Chinese learners whose native language shows no use of double particles. The advanced learners of Korean, regardless of their native languages, showed better judgment on the grammaticality of the use of double particles. This study also found that the type of double particles also affected the learners" judgment and that in the grammaticality judgment of ungrammatical joint of adverbial particles, most of the participants, regardless of their native languages and their Korean proficiency, scored much lower than in the judgment of the other types of double particles. The analyses of the participants" reaction time for the judgment showed congruent results with those of their grammaticality judgement.