Chemical-mechanical polishing (CMP), one of the dominant technology for ULSI planarization, is used to flatten the micro electro-mechanical systems (MEMS) structures. The objective of this paper is to achieve good planarization of the deposited film and to improve deposition efficiency of subsequent layer structures by using surface-micromachining process in MEMS technology. Planarization characteristic of poly-Si film deposited on thin oxide layer with MEMS structures is evaluated with different slurries. Patterns used for this research have shapes of square, density, line, hole, pillar, and micro engine part. Advantages of CMP process for MEMS structures are observed respectively by using the test patterns with structures larger than 1 urn line width. Preliminary tests for material selectivity of poly-Si and oxide are conducted with two types of silica slurries: $ILD1300^{TM};and;Nalco2371^{TM}$. And then, the experiments were conducted based on the pretest. A selectivity and pH adjustment of slurry affected largely step heights of MEMS structures. These results would be anticipated as an important bridge stone to manufacture MEMS CMP slurry.