This study amis to investigate the meanings and the discourse functions of ‘-l su eobs-’ through an examination of the sequences in 21th Sejong Corpus. There have been few research studies of Korean ‘-l su eobs-’ even though the sequence have been considered to have similar function as ‘mos’ negation and play an important role in Korean negation. This study examines ‘-l su eobs-’ and its collocations, using n-gram and phrase-frame analysis. The results are summarized as follows: 1) Overall frequency of ‘-l su eobs-’ is higher than ‘mos’ negation in Korean written corpus. 2) ‘-l su eobs-’ are much more frequently used in double negation than ‘mos’ negation and the antonym ‘-l su iss-’, rather play an strong affirmation function. 3) There seems to be strong correlation between the meanings of ‘-l su eobs-’ and those of ‘-l su iss-’. Examination of 230 examples show that ‘-l su eobs-’ has 2 main meanings [possibility negation], [ability negation].