Aluminum films deposited on air-cleaved and heat-cleaned surfaces of GaAs (110) and GaP (110) were in situ observed by LEED. The substrate temperature lay between 20℃ and 200℃. In systems Al-GaAs the first appearance of the LEED pattern was streaks extending along [001] direction of the substrate in the substrate temperature range from 150℃ to 200℃, the spacing between streaks corresponding to the normal Al-Al interatomic distance. After increasing the thickness {111} facets were formed. The bases of the facets were given to be (112) and (341), (431), the orientation of the former being Al(112)//GaAs(110) and Al[110]//GaAs[110]. At low temperature, only (111) facet was formed, the bases of the facet was drived to be (25 14 1) and (14 25 1). In systems Al-GaP, (111) facet was formed, the base of the facet was drived to be (341) and (431).