In this study, we synthesized 99m Tc(CO) 3 -2′-aminomethylpyridyl-2′-deoxyuridine ( 99m Tc(CO) 3 -AMPDU) and 99m Tc(CO) 3 -aminoethylpyridyl-2′-deoxyuridine ( 99m Tc(CO) 3 -AEPDU) as potential agents for imaging the expression of the non-invasive herpes simplex virus type-1 thymidine kinase. AMPDU and AEPDU were synthesized from uridine in five chemical steps and then labeled with [ 99m Tc(CO) 3 (H 2 O) 3 ] + (370MBq/0.5mL) at 100°C for 10min. Under optimal conditions (0.5 and 1.0mg for AMPDU and AEPDU and heating for 10min), the labeling efficiency was 95.3±2.8% for AMPDU and 94.2±5.1% for AEPDU. To validate the chemical structure of 99m Tc(CO) 3 -labeled compounds, we also synthesized ReBr(CO) 3 -AMPDU and ReBr(CO) 3 -AEPDU by reacting [Et 4 N][ReBr 3 (CO) 3 ] and AMPDU or AEPDU in methanol at 25°C for 6h. 99m Tc(CO) 3 -AMPDU and 99m Tc(CO) 3 -AEPDU had the same retention time on HPLC analysis as ReBr(CO) 3 -AMPDU and ReBr(CO) 3 -AEPDU. 99m Tc(CO) 3 -AMPDU and 99m Tc(CO) 3 -AEPDU had high radiochemical stabilities of 98.1±1.5% and 98.0±1.7% for 6h, respectively.