The defect structures of GaAs film on (001) Si substrate tilted approximately 3-degrees towards the  direction were investigated by the high-resolution transmission electron microscopy. GaAs films were grown by the molecular beam epitaxy (MBE) on the Si (001) substrate by a modified two-step process, in which8 amorphous GaAs buffer layers were grown first. High-resolution electron micrographs show that stacking faults (and/or microtwins) are preferentially formed on the tilted step-rich surface, whereas misfit dislocations are preferentially formed on the flat surface. However, the difference in the defect density on the two cross sections is small. Between the observed 90-degree edge and 60-degree misfit dislocations the density of the latter is higher irrespective of the substrate tilt. This occurrence is explained by the difference in distribution of initial nucleating islands between the present and the conventional two-step MBE techniques.