A heat resistant pneumatic tire whose tread is composed of a rubber composition comprising, as a main rubber component, a modified, conjugated diene based polymer prepared by adding an .alpha., .beta.-unsaturated carboxylic acid represented by the following general formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 independently represent hydrogen atom, halogen atom, or an alkyl, alkenyl or allyl group having at most 5 carbon atoms, or a substituted alkyl, alkenyl or allyl group,to a conjugated diene based polymer in an amount within the range between 0.1% and 5.0% based on the weight of the conjugated diene based polymer. This tire is suitable for continuous running at high temperatures and maintains a good road-surface-grip performance even during such running.