**Abstract**

Photodynamic therapy (PDT) can be used to treat colorectal cancer (CRC). When a photosensitizer (PS) drug is administered to a patient, it can either passively or actively accumulate within a tumor site and once exposed to a specific wavelength of light, it is excited to produce reactive oxygen species (ROS), resulting in tumor destruction. However, the efficacy of ROS generation for tumor damage is highly dependent on the uptake of the PS in tumor cells. Thus, PS targeted uptake and delivery in CRC tumor cells is a crucial factor in PDT cancer drug absorption studies. Generally, within non-targeted drug delivery mechanisms, only minor amounts of PS passively accumulate in tumor sites and the remainder distributes into healthy tissues, causing unwanted side effects. To improve the efficacy of PDT research is currently focused on the development of specific receptor based photosynthetic nanocarrier platform drugs, which promote the active uptake and absorption of PS drugs in CRC tumor sites only, avoiding unwanted side effects, as well as treatment enhancement. This chapter will focus on current actively targeted PS nanoparticle drug delivery systems, which have been investigated for the PDT treatment of CRC cancer.

**Keywords:** colorectal cancer, photodynamic therapy, photosensitizer, nanoparticles, targeted drug delivery
