To improve the solubility and dissolution rate of trimethoprim (TMP), which is slightly soluble drug, its inclusion complexes were prepared and studied in this experiment. Inclusion complexes of TMP with ${eta}-cyclodextrin$ and ${eta}-cyclodextrin$ polymer (CDPS) were prepared according to Fenyvesi method. These were compared with TMP and its physical mixture with CDPS. Water, diluted hydrochloric acid and phosphate buffer solution were used as dissolution media. And accelerated stability test was studied at $50,;70;and ;80^{circ}C$. It was found that solubility and dissolution rate of inclusion complexes were increased in water. Especially, the solubility and dissolution rate of TMP was found to be markedly increased by inclusion complexation with CDPS. In stability test, ${eta}-cyclodextrin$ inclusion complexes were more or less stable than TMP alone. This tendency was not led in CDPS. Consequently, CDPS was useful in increasing dissolution rate and stability of TMP.