Towards the development of a thermosensitive drug-delivery vehicle for nasal delivery, a systematic series of N-trimethyl chitosan chloride polymers, synthesised from chitosans of three different average molecular weights, have been co-formulated into a hydrogel with poly(ethylene glycol) and glycerophosphate. Rheological evaluations have shown that hydrogels derived from N-trimethyl chitosan with a low degree of quaternisation and high or medium average molecular weight exhibit relatively short sol–gel transition times at physiologically relevant temperatures. Also, the same hydrogels display good water-holding capacity and strong mucoadhesive potential, and their mixtures with mucus exhibit rheological synergy. An aqueous hydrogel formulation, derived from N-trimethyl chitosan of medium average molecular weight and low degree of quaternisation, appears particularly promising in that it exhibits most favourable rheological and mucoadhesive behaviour and a sol–gel transition that occurs at 32.5 °C within 7 min.