A high energy electron irradiation-photoluminescence (PL) technique is employed for developing an analytical method for determining the concentration of carbon in silicon crystals. Particular attention is paid to the effect of oxygen concentration on the PL intensity. The intensity of the 0.790 eV PL peak (C-line) due to the complex C-l-O-l (I : interstitial) formed by electron irradiation can be used to measure the lowest levels of 10(14) to 10(15) atom/cm(3) of carbon, almost independently of oxygen concentration. The intensity of the 0.969 eV peak (G-line) due to the complex C-s-Si-l-C-s (S : substitutional) is highly affected by the oxygen concentration. When the oxygen concentration in the crystal is known, by using this peak, carbon concentrations or 10(16) to 10(17) atom/cm(3) can be determined within an uncertainty of +/-30%. By using both PL peak intensities and theoretical curves obtained from the rate equations of the complex formation, it is possible to determine carbon concentrations in the 10(14) to 10(17) atom/cm(3) range.