Abstract: Biological immunotherapy using checkpoint inhibitors has evolved into a promising therapy for cancer patients. Unfortunately, not all patients respond to the therapy while severe immune-related adverse effects are prevalent. Molecular imaging can detect the expression of immune checkpoint (IC) at the molecular and cellular level in tumor microenvironment. It can help in selecting patients who are suitable for immunotherapy, and also monitor the tumor response. This paper reviews the current status and latest progress of molecular imaging of IC targets.