We have made a new investigation on the vertical profiles of tritium and helium isotopes in Lakes Van and Nemrut(Eastern Turkey),using experimental data from the reference by Kipfer et al.for study of long-term vertical mixing and deep water renewal in Lake Van.Lakes Van and Nemrut are crater lakes.Lake Nemrut is at the western border of Lake Van.The 3He and 4He are injected at the bottom of Lakes Van and Nemrut,and the both helium isotopes are confirmed from the mantle source.From 3H(tritium) data in Lakes Van and Nemrut,we have observed “3H anomaly” at the vertical profile of 3H concentrations in Lake Nemrut.The 3H concentration at the lake bottom is 10% higher than at the surface.The difference of 3H concentrations between surface and bottom is about 3.7±1.2 TU.This excess 3H should be injected from the lake bottom.An investigation on the origin of the injected tritium has been made.The results show the conventional origins are excluded,such as residence of precipitation tritium from nuclear testing in the early 1950s-1960s and tritium from known nuclear reactions.Based on the correlation of excess 3H with 3He and heat flow in Lake Nemrut,we infer that the 3He and 3H might be all from the mantle source,and produced by the supposed natural-nuclear-fusion,which might occur in an environment rich in water(H) and(U + Th) at high temperature and high pressure in the deep Earth.Detection of tritium in the Earth’s interior is a key evidence for exploration of natural nuclear fusion in the deep Earth.Based on the published data,we have found that the excess 3He and 3H injected at the bottom of Lake Laacher(Germany) were also released from the mantle source.The present work will be helpful to the further study of mechanism of natural nuclear fusion in the Earth’s interior. We have made a new investigation on the vertical profiles of tritium and helium isotopes in Lakes Van and Nemrut (Eastern Turkey), using experimental data from the reference by Kipfer et al. For study of long-term vertical mixing and deep water renewal in Lake Van.Lakes Van and Nemrut are crater lakes. Lake Nemrut is at the western border of Lake Van. 3He and 4He are injected at the bottom of Lakes Van and Nemrut, and the both helium isotopes are confirmed from the mantle source. Fe 3H (tritium) data in Lakes Van and Nemrut, we have observed “3H anomaly ” at the vertical profile of 3H concentrations in Lake Nemrut. 3H concentration at the lake bottom is 10% higher than at the surface. The difference of 3H concentrations between surface and bottom is about 3.7 ± 1.2 TU.This excess 3H should be injected from the lake bottom. An investigation on the origin of the injected tritium has been made. The results show the conventional origins are excluded, such as residence of precipitation tritium from nuclear testing in the early 1950s-1960s and tritium from known nuclear reactions. Based on the correlation of excess 3H with 3He and heat flow in Lake Nemrut, we infer that the 3He and 3H might be all from the mantle source, and produced by the supposed natural-nuclear-fusion, which might occur in an environment rich in water (H) and (U + Th) at high temperature and high pressure in the deep Earth. Detection of tritium in the Earth’s interior is a key evidence for exploration of natural nuclear fusion in the deep Earth. Based on the published article, we have found that the excess 3He and 3H injected at the bottom of Lake Laacher (Germany) were also released from the mantle source. The present work will be helpful to the further study of mechanism of natural nuclear fusion in the Earth’s interior.