The Western Himalayan state of Uttarakhand in India is represented five species of oaks of the genus Quercus that are important from conservation as they support rich biodiversity of fauna and also for their multiple utilization values for local communities living in the region. However, oak forests today are under threat of extinction today mainly due to anthropogenic pressures along with attack by many species of insects.  Hence, there is a need to know the insect pest spectrum of oak forests and identify those species can cause damage to these trees, directly. As such field surveys across the oak forests of the state were carried out for 3 years (2017-2020) and revealed 114 species of insects infesting these 5 species of oaks. The comprehensive annotated checklist of insects infesting western Himalayan oaks in the state was prepared for 235 species (119 Lepidoptera; 100 Coleoptera; 16 Hemiptera & 1 Diptera) so far recorded on them and is presented in this paper along with their classification, habit, month of incidence and species of oak tree infested. Break up of species in different families of each of these 4 orders recorded is given along with species capable of causing potential damage to oak trees.