Over 90% of the paved roads in Canada are asphalt pavements. Most of the pavements were built decades ago and are currently exhibiting a significant amount of surface distresses. These distresses include potholes, rutting (deformation in the wheel path), and cracking. To repair these old pavements, the road agencies spend millions of dollars every year, of which a major portion goes to acquire new natural aggregates and asphalt. To reduce this cost, road agencies use up to 100% reclaimed old asphalt pavements (RAP) in new construction. However, the asphalt available in recycled pavements are already oxidized and stiffened due to various environmental processes which is susceptible to thermal and fatigue cracking. Addition of rejuvenator can decrease the viscosity and soften the RAP materials by reactivating and restoring the original properties of asphalt binder. Waste Cooking Oil (WCO), which contains the similar lighter oil components of asphalt, can be used as a good rejuvenator in this regard. Recent studies showed that, WCO has an excellent potential to be used as a good rejuvenator in HMA industry. This review article summarizes the performance and negative effects of WCO in asphalt binder performance and HMA.