The xand Q2-dependences of the Gottfried sum rule SG(x,Q 2) based on the experimental data on proton and deuteron structure functions are studied. The dependence of SG(x,Q 2) on Q2 for low x points to flavour asymmetry of sea quark distributions. For the first time, the coefficients c1, c2 of the expansion of SG(x,Q 2) in αS/π up to second order are evaluated through the phenomenological analysis of NMC and H1 data. It is found that c1 is negative while c2 is positive. The obtained result is in disagreement with QCD predictions for these coefficients. We suggest measuring the low x-dependence of the FD 2 deuteron structure function at HERA in order to study the Q2-dependence of the Gottfried sum rule.