The present invention provides an application of AKR1C1, AKR1C2, or AKR1C3 for use as a biomarker for predicting drug sensitivity in the treatment of cancers with gemcitabine or a pharmaceutically acceptable salt thereof. The cancers being colon, lung, gastric, pancreatic, ovarian, melanoma, liver, breast, and cervical. By adopting the technical solution of the present invention to guide clinical medication, blindness in drug selection can be avoided, thus avoiding treatment delays due to improper drug selection, and therapeutic effect of drugs can be monitored during treatment processes, achieving the objective of appropriate drug use and individualized treatment.