This paper investigated the use of of, the most frequently occurring preposition, in essays written by 416 matriculants at a Korean university. The learner corpus consisting of these essays contained 1,250 tokens of of, and these tokens were first analyzed according to their functions, i.e., integrative, separative, idiomatic, and others, adapted from Lindstromberg’s (2010) categorization of the functions of of. To ascertain what types of errors were made regarding of, the 46 tokens of of identified as errors were further categorized as addition, misordering, misformation, or wrong position. Of these four categories, addition was found to be the most frequently occurring type of error (31 of the 46 tokens), while wrong preposition and misformation accounted for ten and three tokens, respectively. No tokens of misordering were found, however. Also noteworthy is the finding that, albeit occurring mostly in simple constructions and basic functions, of was used accurately in over 95% of all the tokens found in the learner corpus.