We performed small-angle X-ray scattering (SAXS) measurements on crystallization processes of polyethylene blends of low molecular weight and ultrahigh molecular weight components with various blending ratios in order to clarify effects of ultrahigh molecular component on shish-kebab structure formation. Anisotropic scattering patterns due to kebab structure formation were observed above a certain concentration of ultrahigh molecular weight polyethylene. The critical concentration was about similar to 0.1 wt % independent of the crystallization temperature below 125 degrees C, while it increased with the crystallization temperature above 125 degrees C. Analyzing the correlation between ultrahigh molecular weight component concentration and crystallization temperature in more detail, these results suggest that both the crystallization rate and the relaxation rate of the ultrahigh molecular weight component have significant effects on the shish-kebab formation process.