Bitumen is a typical binder for road construction applications. The length of pavement life cycle is decreasing as the frequency and heavy duty transport is increasing. Therefore there is a demand for binders with superior physico-mechanical properties that would make roadway more resistant to the growing transport loading. The best option how to improve overall properties of bituminous binders is to apply various additives or modifiers. The most advantageous modifiers are polymer based materials. The target characteristics of polymer modified binders include higher elastic recovery, higher stiffness, longer lifetime, etc. The modification of bituminous binders is used to improve their performance properties. The effect of polyphosphoric acid (PPA) on physico-mechanical properties was investigated using various rheological tests. The bituminous binders modified by PPA showed higher stiffness at high temperatures and improved thermal stability keeping the same or slightly improved low-temperature properties.