The solubility and stability of ondansetron hydrochloride (OS) in various vehicles were determined. The effect of cyclodextrins (CD) on the solubility of OS in water was determined by equilibrium solubility method. The solubility of OS at $32^{circ}C$ increased in the rank order of isopropyl myristate (IPM) < propylene glycol laurate (PGL) ${ll}$ propylene glycol monolaurate < propylene glycol monocaprylate (PGMC) < poly(ethylene glycol) 400 < diethylene glycol mono ethyl ether (DGME) < ethanol < poly(ethylene glycol) 300 < water (36.1 mg/ml) ${ll}$ propylene glycol (PG) (283 mg/ml). The addition of PG or DGME to non-aqueous vehicles such as IPM, PGL and PGMC markedly increased the solubility of OS. The addition of CDs in water increased the solubility. Apparent stability constant for the CD complexation with OS was calculated to be $25.5;M^{-1}$ for $2-hydroxypropyl-{eta}-CD;(2HP{eta}CD)$. Twenty mM ${eta}-CD$, 69.4 mM sulfobutyl ether ${eta}-CD$ and 115.4 mM $2HP{eta}CD$ increased the aqueous solubilty of OS 1.27, 2.18 and 1.85 times, respectively. OS was stable in buffered aqueous solution (pH 5.0). However, OS was relatively unstable in non-aqueous vehicles in the order of PG<DGME<PGMC-DGME(60 : 40) co-solvent<PGMC. The degradation of OS in these vehicles was accelerated, depending on temperature.