Abstract A new method for the absorption correction of EDX analysis in the TEM including low-energy X-ray lines was applied. The Cu/O mole fraction ratio for YBa 2Cu 3O 7- x ceramics was determined quantitatively using CuO as standard. Preliminary experiments were carried out to investigate the absorption behaviour (as a function of specimen thickness) of the low-energy X-ray lines (O-K and Cu-L) in CuO, YBa 2Cu 3O 7- x and (Bi, Pb) 2Sr 2Ca 2Cu 3O 10+δ. These experiments confirmed the general estimation that flourescence effects are negligible for the transition metal/O mole fraction determination of transition metal oxides by EDX in the TEM. By a combination of EDX and EELS measurements and a thickness determination applying the trace method on (001) twin boundaries in CuO, the Cu mass absorption coefficient for the O-K line could be refined. The tabulated value was found to be too large by a factor of 2. The strength of the applied method (with respect to the usually applied k-factor analysis) is that transmission coefficients are determined experimentally. Thus, the thickness of the specimen areas, at which spectra are acquired, as well as the mass absorption coefficients need not be known for quantitative EDX analysis.