Inclusion complexes of diclofenac sodium with ${eta}-cyclodextrin$ were prepared in aqueous solution, alkaline solution and solid phase. The interaction of diclofenac sodium with ${eta}-cyclodextrin$ in pH 9.0 alkaline solution was evaluated by the solubility method and the instrumental analysis such as thermal analysis, infrared spectroscopy, X-ray diffractometry. The solubility of diclofenac sodium was increased linearly with the increase in the concentration of ${eta}-cyclodextrin$up to 0.15 mol and showed that the aqueous solubility rate of diclofenac sodium was significantly increased by complex with ${eta}-cyclodextrin$. The optimum composition of this complex was one molecule of ${eta}-cyclodextrin$ included 1.59 molecular weight of diclofenac sodium as a guest molecule. The pharmacokinetic parameters of the diclofenac sodium and the complex with ${eta}-cyclodextrin$ were studied in rats by oral route. $T_{max}$ between drug alone and inclusion complex showed significant difference to be 120 minute and 20 minute respectively. Both of $C_{max}$ and AUC of inclusion complex was about 40% higher than drug alone. It is estimated from the data in this study that complexation of diclofenac sodium with ${eta}-cyclodextrin$ increased the absorption rate and improved the bioavalability of the diclofenac sodium by the formation of a water-soluble complexes.