ProTide and cyclic phosphate ester are two successful prodrug technologies to overcome the limitations of nucleoside drugs, among which the cyclic phosphate ester strategy has not been widely used in the optimization of gemcitabine. Herein, we designed a series of novel ProTide and cyclic phosphate ester prodrugs of gemcitabine. Cyclic phosphate ester derivative 18c exhibits much higher anti-proliferative activity than positive control NUC-1031 with IC50s of 3.6-19.2 nM on multiple cancer cells. The metabolic pathway of 18c demonstrates that 18c's bioactive metabolites prolong its anti-tumor activity. More importantly, we separated the two P chiral diastereomers of gemcitabine cyclic phosphate ester prodrugs for the first time, revealing their similar cytotoxic potency and metabolic profile. 18c displays significant in vivo anti-tumor activity in both 22Rv1 and BxPC-3 xenograft tumor models. These results suggest that compound 18c is a promising anti-tumor candidate for treating human castration-resistant prostate and pancreatic cancer.