This study defines, the term “expectancy grammar” proposed, by Oller (1979), as the ability to process the language information, and predict the appropriate language elements for a given situation. The Japanese conditionals, BA, TO, NARA, and TARA, were used for the data analysis to investigate expectancy grammar between learners of Japanese (LJ) and native speakers of Japanese (NSJ). The participants in this study were asked to complete sentences in response to two different types of questions. The following results were obtained: 1) NSJs showed consistency when answering some questions but not all. The results were in agreement with those obtained by NSJs. 2) the higher levels of language in LJs contained fewer grammatical errors than the lower level. No grammatical errors were observed at both levels in some questions. 3) word usage was inconsistent between different questions when answered by both NSJs and LJs. LJs’ word choice completely differed from that of NSJs, based on cultural background shown only in LJs’ group.