Dantrolene sodium (Da) is an effective skeletal muscle relaxant. However, its pharmacological effects are severely limited owing to its poor solubility and low oral bioavailability. In order to solve these problems, an inclusion complex using hydroxypropyl-β-cyclodextrin (HP-β-CD) to improve the oral bioavailability of Da was prepared successfully by freeze-drying. The prepared complex was characterized by Powder X-ray diffractometry (PXRD), Fourier transform infrared spectroscopy (FTIR) and evaluated by a dissolution test and a pharmacokinetic study. The results of PXRD and FTIR proved the formation of a complex between Da and HP-β-CD. The dissolution rate of Da was markedly improved from inclusion complex with more than 90% being released within 5 min. The in vivo pharmacokinetics of Da and dantrolene sodium-hydroxypropyl-β-cyclodextrin (Da-HP-β-CD) inclusion complex were investigated in rats using a UPLC/MS/MS method. The Cmax and AUC0-t of the Da-HP-β-CD inclusion complex were 5- and 3-fold higher than that of the Da. These results suggested that the Da-HP-β-CD inclusion complex markedly improved the dissolution rate and bioavailability of Da.