This paper explores the method for Korean text watermarking and develops a syntactic tree-based adverbial displacement scheme. Korean, as an agglutinative language, provides a good ground for the syntactic tree-based natural language watermarking because syntactic constituent order is relatively free –especially syntactic adverbial. Our proposed natural language watermarking method consists of six procedures. First, we construct a syntactic dependency tree of unmarked text. Next, we perform clausal segmentation from the syntactic tree. Third, we choose a target adverbial constituent, which will be displaced within its clause. Then, we embed a watermark bit. Fifth, if the watermark bit does not coincide with the direction of the target adverbial displacement, we displace the target adverbial constituent in the syntactic tree. Finally, from the modified syntactic tree, we obtain a marked text. From the experimental results, we show that the coverage of our method outperforms that of previous systems, and the rate of unnatural sentences of marked text is better than that of previous systems. Experimental results also show that the marked text keeps the same style, and it also has the same information without semantic distortion.