This study analyzes the meaning of toki and baai in Japanese sentences. The purpose of this study are to find out the meanings of toki and baai, similarities and differences in the meaning of toki and baai at sentences, as well as the possibility of toki and baai able to replace each other in the same sentence. This study uses a descriptive method with a qualitative approach. The data collected by notes and literature review (literature study). The research subject focused on toki and baai in Japanese textbooks. Based on the results of data analysis, toki means ‘at (time)’, ‘time’, ‘when’. The meaning of toki indicates the occurrence of events and relate to time. Baai means ‘if’, ‘case’ or ‘in case of’. The meaning of baai contextually shows the existence of presuppositions in situations and indicates certain conditions. The meaning of toki and baai are to indicate an event or situation in terms of a certain time. The difference in the meaning of toki and baai, namely toki indicates of event or activities in terms of time. baai indicates the presupposition of the situation in specific times. Noun of toki and baai can replace each other depending on the context of the sentence used. Toki can be replaced in the context of a sentence that indicates a situation or occurence. Baai can be subtituted with toki that indicates the existence, activity, occurence or situation in sentence. However, baai cannot replace toki if the context of the sentence shows a personal experience and using past tense.