Studies on the role of input in L2 acquisition often estimate L2 input properties through L1 corpora and focus on L2-English. This study probes the initial stage of L2-Korean learning for adult English-speaking beginners of Korean to investigate input-output relations in the acquisition of L2 that is typologically different from English in a more direct manner. We specifically ask how L2 beginner input affects L2 beginner production with respect to Korean postpositions. For this purpose, we investigate how the beginners receive input regarding Korean postpositions from a textbook and to what extent the input characteristics are manifested in learner writing. We found that, whereas the presentation of certain postpositions in the textbook was generally reflected in learner writing, individual postpositions showed disparity in their use between the textbook and the writing. Implications of the findings are discussed in light of L1-L2 differences and how the textbook presents form-function pairings of these postpositions.