The rate of return of education on wage is a well-known problem in economics since the 60's with the works of G. Becker and J. Mincer. The present master thesis discusses one of the main assumption of Mincer equation: the linearity of the rate of return of education. Working on the FQP 2003 dataset of the INSEE, we show that with an appropriate specification, an educational year leading to a degree has a higher rate of return than another without diploma.