Abstract: The effect of ratio of calcium to sulfur on hot deformability of sulfides in the gear steel 18CrNiMo7-6 after calcium-treatment was investigated by means of optical microscope,scanning electron microscope and electron spectrometer.The results show that the sulfides were composed of single phase sulfide and oxide-sulfide duplex inclusions in steels when the ratio was between 0.019 and 0.068.The content of the compound inclusions correlated proportionally with the ratio of the steel,and the relative plasticity of all sulfides decreased linearly with the ratio.The relative fraction and composition of oxide-sulfide compound inclusions which were influenced by the ratio played a major role in relative plasticity for all sulfides.