A method of deriving the travel time of drip water based on the tritium/helium 3 (3H/3He) dating method was demonstrated in limestone caves in Indonesia. The examined drip waters from two caves, which were taken using different methods, included 2.15 (± 0.84) TU and 1.35 (± 0.77) TU of tritiogenic 3He. From the derived tritiogenic 3He contents and the measured tritium concentrations of the drip water samples (2.02 ± 0.27 TU and 1.19 ± 0.40 TU), the 3H/3He ages (travel times) of the drip waters from the two caves were estimated as 12.9 ± 3.8 years and 13.5 ± 6.3 years. The latter age is probably overestimated because re-equilibration of He between drip water and cave air is expected to occur during sampling. For reliable derivation of 3H/3He age, it is advisable to take a drip water sample that is kept isolated from the cave air.