The input and decomposition of litter, and the C/N ratio evolution was studied for 2 years in evergreen oak forests in the Catalonian Central Basin. The decay constant, k, obtained was 0.365. The C/N ratio had a sharp decrease in the initial 7 months of decay, then it reached an equilibrium value of 22-23, which remained constant during the period of incubation. In this 7-months period, there was a strong N immobilisation by the microorganisms; afterwards, there was N mineralisation because it had to be the same rate of C and N loss to keep the C/N ratio nearly constant. From the comparison between the incubation in litter bags and the per cent C and C/N ratio distribution in the soil profile, it is concluded that the L horizon had an age of about 7 months and the F1 horizon had a turnover rate of 1.5 years.