Title of a research article is an abstract of the abstract. Titles play a decisive role in convincing readers at first sight whether articles are worth reading or not. Not only do research article titles show how carefully words are chosen by authors, but also reflect disciplinary differences in terms of title words and structure between hard sciences and soft sciences. This study examined the lexical density and syntactic structure of 690 research article titles chosen from five Library Science and Scientometrics journals, aiming to reveal disciplinary differences. The result suggested both Library Science and Scientometrics have almost the same title length and the prevalent usage of Nominal Phrase (NP) to govern the title structure. The result also stated some disciplinary differences: Library Science demonstrates more punctuation complexity, particularly a greater frequency in using colons; but Scientometrics shows more involvement of words related to research methods, which is an indicator to papers’ scientific value, and more usage of declarative Full Sentence (FS) structure, which were mostly discovered in the research articles in hard sciences.