Candesartan-cilexetil, an angiotensin receptor blocker, exhibits low bioavailability after oral administration due to its low water solubility. Chitosan is considered one of the most promising biopolymers for drug delivery as a vehicle and trimethyl chitosan is a water soluble chitosan derivative. Trimethyl chitosan nanoparticles were prepared by the ionic crosslinking of a trimethyl chitosan solution with tripolyphosphate, at ambient temperatures during stirring. SEM and TEM (scanning and transmission electron microscopy) revealed trimethyl chitosan and trimethyl chitosan nanoparticles between 1,000-3,000 nm and 13-350 nm in size, respectively. Candesartan-cilexetil was loaded on trimethyl chitosan nanoparticles, trimethyl chitosan, gum arabic and commercial water soluble chitosan using an ultrasonic effect, and the potential of the polymers to increase the solubility of candesartan-cilexetil was investigated. Trimethyl chitosan nanoparticles are a superior vehicle for increasing the solubility of candesartan-cilexetil compared to trimethyl chitosan, gum arabic or commercial water soluble chitosan.