This study investigates the grammatical skills of typically developing Oromo-speaking preschool-age children and lays the foundation for a language assessment tool for Oromo, a Cushitic language spoken in Ethiopia. The current study used a standard picture-based elicitation task that evaluated children's accuracy in producing grammatical utterances. Language samples were collected from 44 monolingual 3- to 4-year-old Oromo children with typical language development. The percentage of grammatical utterances (PGU) was computed and error types were analyzed. The average level of grammatical accuracy as measured by PGU was 69%, with a large amount of variability. The data for Oromo 3-year-olds showed a variety of infrequent error types. The results of the study provide crucial foundational knowledge on grammatical development in Oromo, which could form the basis of future language assessments and diagnostic materials.