Public speaking can be very threatening to any native speakers of English, not to mention non-native EFL learners. Impromptu speech, perhaps the most challenging form of public speaking, is however being promoted in every city of the EFL countries. The case in Taiwan is no exceptional. Every year, dozens of impromptu speech contexts are held throughout the island. Over the past decade, many studies have investigated the strategies and techniques successful EFL impromptu speech contestants adapted. Hardly has any study touched upon the language used by the prize-winning contestants. Also at the same time, a growing number of studies on second language speaking acquisition have pinpointed that multiword lexical units (i.e., lexical collocations, fixed-/semi-fixed expressions, and idioms) could be the key to better speaking proficiency. Therefore, the study intends to examine the possible relationship between MLUs and impromptu speeches. Data of the current study draws on the biggest annual national impromptu speech contest of Taiwan where EFL contestants competed to show their language proficiency as well as skills in delivering spoken messages. The 11 participants are English majors of technological universities in Taiwan and have never lived in an English speaking country for more than 6 months. In the contest, each contestant selected a topic 15 minutes before going on the stage, and each had 3 minutes to deliver a speech in English. The researcher video-taped, transcribed, and analyzed all the impromptu speeches. The data were examined to answer the three research questions for correlations: (1) between the subjects' performance of impromptu speeches and their use of lexical collocations; (2) between the subjects' performance of impromptu speeches and their use of fixed-/semi-fixed expressions; and (3) between the subjects' performance of impromptu speeches and their use of idioms. By examining the correlations between MLUs and impromptu speeches, this study aims to find an additional way to help EFL learners to become a better speech constant in particular and improve college EFL learners' speaking proficiency in general. (Contains 4 tables and 6 footnotes.)