Folate‐conjugated fluorescent silica–gold nanoparticles (FSGNs‐F) and radioactive gold nanoparticles [S(198Au)GNs‐F] were prepared and evaluated for the detection of folate‐receptor‐overexpressed cancer. Fluorescence imaging showed that FSGNs‐F was targeted successively to mouse colon carcinoma cells (CT‐26, folate receptor positive), whereas vague localization was observed in human lung adenocarcinoma epithelial cells (A549, folate receptor negative). S(198Au)GNs‐F also targeted CT‐26 cells in a time‐dependent manner: 35.2 ± 1.20% at 15 min, 39.3 ± 1.95% at 30 min, 41.6 ± 1.62% at 60 min, and 49.8 ± 1.22% at 120 min. In addition, the biodistribution of S(198Au)GNs‐F showed significant uptake in CT‐26 tumors with 0.58 ± 0.02 and 0.42 ± 0.02 %ID/g at 60 and 120 min, respectively. The tumor to blood ratio was 2.18 at 120 min after the injection. These results suggest that S(198Au)Ns‐F has potential as a folate‐receptor‐targeted agent.