We investigate the variation in coronal activity of late-type stars with age. We determine the age of the star from the colour-colour diagram (U-B vsB-V). We show that the ratio of X-ray luminosity (Lx) to bolometric luminosity (Lbol) is well correlated with age over several orders of magnitude variations. We find thatLx/Lbol) decreases with age with a power of −1.55. This is consistant with the expected results from the studies of the variation of the corona with chromosphere and the dependence of chromosophere on age.