Using the oscillation frequencies of alpha Cen A recently discovered by Bouchy & Carrier (2001, 2002), the available astrometric, photometric and spectroscopic data, we tried to improve the calibration of the visual binary system alpha Cen. With the revisited masses of Pourbaix et al. (2002) we did not succeed in obtaining a solution satisfying all the seismic observational constraints. Relaxing the constraints on the masses, we have found an age t(alphaCen) = 4850 +/- 500 Myr, an initial helium mass fraction Y-i = 0.300 +/- 0.008, and an initial metallicity (Z/X)(i) = 0.0459 +/- 0.0019, with M-A = 1.100 +/- 0.006 M-. and M-B = 0.907 +/- 0.006 M-. for alpha Cen AB.