A summary of the knowledge about petrography and geology of E Nepal Himalaya and the results of 15 age determinations by the K/A method on samples from very different tectonic units of this area, are given in this paper. The results show that: I. The end of the Alpine (Himalaya) metamorphism in E Nepal takes place at the end of Miocen or beginning of Pliocen (about 13 M. a.). II. A Precambrian metamorphism is brought up by the K/A age of a detrital muscovite separated from a non metamorphosed quartzite. III. The K/A ages of catazonal rocks are younger than those of epizonal origin. An hypothesis is given to explain this particular point.