The siliconized layer on low silicon steel substrate was produced under pulse current conditions from KCl-NaCl-NaF-SiO2 molten salt and the effects of frequency on the composition and microstructure were investigated. The results showed that at the same average current density and other experimental conditions, Si content in the surface and the layer thickness decreased with increasing frequency. Low pulse frequency (500 Hz) and high frequencies (1500, 2000Hz) produced coarse grain and bigger surface roughness. There was a flat fine grain structure and a relatively thick (30m) layer when the frequency was 1000Hz. However, the effect of pulse frequency on the structure of the layer was not obvious. The phase structure of the layer was composed of Fe3Si with (110) preferred orientation at all experimental frequencies.