ABSTRACT: The goal of this paper is to provide a descriptive account of the grammar of the particle ojo in Javanese, which is known to be the tenth largest language in the world with over 70 million speakers in Indonesia, but vulnerable to endangerment. Hence, this study is an attempt to contribute in documenting the grammar of Javanese. The data underlying the study come immediately from elicitations to Javanese-speaking correspondents. We argue that ojo is used in Javanese as an auxiliary verb that has the function of expressing prohibition. It has been found that ojo precedes or follows the finite verb it accompanies, which is prefixed with a nasal affix. The subject of the clauses containing the item under examination is required to show up only if it is not a second person. In different kinds of predicates ojo can be used, including single-root verbs, reduplicated verbs, adjectives, prepositional phrases, and nouns. Ojo does not co-occur with the majority of the auxiliaries, especially those with temporal reference and those expressing necessity of doing actions.