Abstract: For the evaluation of the early effect of different therapies for the treatment of malignant tumors, reduction in tumor volume is the most commonly used criterion for efficacy. However, the time until tumor shrinkage can be long and it requires repeated tumor volume measurements several times weekly to show effect. Non-invasive method such as PET allows for biological processes to be visualized and quantified non-invasively over time, and it has a high specificity for the early diagnosis, staging and evaluate the response of tumors. ¹⁸F-FDG is the most widely used radiotracer for imaging in oncology and is very useful for detecting and characterizing cancers currently. But it is not a tumor specific agent for the intrinsic property. 3′-deoxy-3′-¹⁸F- fluorothymidine(¹⁸F-FLT) is used as a PET tracer for visualization of cell proliferation and it has become more widely used in clinic. Both of them have their own features in the diagnosis, staging and early detect response of tumors. This article reviewed the application of ¹⁸F-FDG and ¹⁸F-FLT to evaluate the early response of malignant tumors after different therapies. Besides, at the same time, ¹⁸F-FDG and ¹⁸F-FLT which is more specific or superiority to measure early response of tumors after definite treatment was discussed.