The doctrine of reincarnation in Tibetan Budhism is a secret teaching and very hard to understand, especially from the modern point of view. The purpose of this thesis is to comparatively study this doctrine with the doctrine of rebirth in Theravada Buddhism. From the study, it is found that the doctrine of reincarnation in Tibetan Buddhism states that a bodhisattva who has completed the practice of Highest Yoga Tantra or Highest Yoga Mantra is able to reincarnate as he will. The bodhisattva who has successfully meditates in the clear light of death or prapassvara mind will the Buddhahood or the Truth Body. One who successfully meditates in the intermediate state will attain the Enjoyment Body. Other who successfully meditates in the state of taking birth will attain the Emanation Body. With the vows of that spring from compassionate mind to help sentient beings to liberate from suffering of samsara, those bodhisattvas who attain the dharma will reincarnate in world. Through the powers of the vows, they can meditate to reincarnate with awareness in the mothers’ wombs in the human world, not forced by karma, like ordinary people.
