In writing, combining sentences is intended to make some sentence varieties; one of the varieties could be used is sentences based on clause structure. In English Department of FKIP ULM, students mostly use the simplest form of sentences rather than the other forms of sentences in their compositions. This condition led the researcher to conduct a research to find out the 6^th semester students’ ability in creating sentences based on clause structure at English Department of FKIP ULM.

Descriptive and mixed methods research was used as the research design. To find out the students’ ability, test was used as instrument. Students who are in the 6^th semester at English Department had to create 40 sentences which were divided into 4 parts: creating simple sentences, compound sentences, complex sentences, and compound-complex sentences. To show which category the students’ ability in creating sentences based on clause structure, the score of students would be categorized into some ability classifications.

Based on the findings, the students’ ability in creating sentences based on clause structure was categorized into poor category (53.9). Then, students’ ability in creating sentences for each type was excellent for simple sentences (88.9), fail for compound sentences (49.6), almost good for complex sentences (66.9), and fail for compound-complex sentences (31.8).

From the result of this research, it is suggested for the lecturer to give more exercises about sentences based on clause structure from the simplest form until the most complicated form and encourage students to use those varieties of sentences in writing. For students, it is suggested to keep practicing and read more to enrich their knowledge. It will be useful to improve their writing skill and grammar mastery.   

Key words: ability, sentences, clause structure