Null object (NO) constructions in Korean and Japanese have received different accounts: as (a) argument ellipsis (Oku 1998, S. Kim 1999, Saito 2007, Sakamoto 2015), (b) VP-ellipsis after verb raising (Otani and Whitman 1991, Funakoshi 2016), or (c) instances of base-generated pro (Park 1997, Hoji 1998, 2003). We report results from two experiments supporting the argument ellipsis analysis for Korean. Experiment 1 builds on K.-M. Kim and Han’s (2016) finding of interspeaker variation in whether the pronoun ku can be bound by a quantifier. Results showed that a speaker’s acceptance of quantifier-bound ku positively correlates with acceptance of sloppy readings in NO sentences. We argue that an ellipsis account, in which the NO site contains internal structure hosting the pronoun, accounts for this correlation. Experiment 2, testing the recovery of adverbials in NO sentences, showed that only the object (not the adverb) can be recovered in the NO site, excluding the possibility of VP-ellipsis. Taken together, our findings suggest that NOs result from argument ellipsis in Korean.