The dating of the Galaxy is a basic task in modern astrophysics. One method of estimating the age of the Galaxy is nucleo-cosmochronology. The idea of such a chronometry is to determine the age of individual stars by comparing the change of the abundance ratio with time  between a long-lived radioactive element and a stable element in the oldest stars. The present ratio of the element pairs, derived from the stellar spectrum, is compared with the initial abundance ratio at the time of the star formation, predicted from a theoretical model. At first, this age-dating approach was used to estimate the age of G-dwarf stars with Th/Nd chronometry. Recently, it has been used to evaluate the age of halo field stars and globular cluster stars with the Th/Eu and U/Th chronometers. We first briefly introduce the principle of this approach, and then review the history of Th and U abundance study in stars, with emphasis on the extremely metal-poor halo stars. The reliability of this technique and the uncertainties in the age estimate are well discussed. As comparison, other methods of dating the Galaxy are briefly introduced. Some further investigations are suggested at last.