<p>Cancer is one of the leading causes of death worldwide and in most cases difficult to treat. Exposure to high doses of conventional therapy (e.g., radiation, chemotherapeutic agents) often leads to significant toxicity in normal cells due to non-specific targeting. To overcome these issues, attention has focused on the use of nanoparticles for the delivery of drugs to tumor cells. In particular, phytochemicals, which are extracted from plants, have shown to be attractive therapeutic agents for fighting against biological resistance towards cancer treatment. As many of these natural constituents are poorly soluble, their bioavailability can be significantly improved through nanoparticle loading. The present review highlights some of the important phytochemicals used for cancer and the methods available for their extraction and separation. The different strategies for constructing phytochemical-loaded nanoparticles are explained followed by an overview of the different techniques commonly used for characterizing the physical and chemical properties of these nanoparticles (e.g., size, surface charge). The structure and composition of nanoparticles play an important part in their tumor accumulation and internalization in cancer cells. Different types of phytochemical-based nanoformulations are discussed for treating different cancer types, with results presented from both in vivo studies and clinical trials.</p>