Qara Aqaj titanium potential is one of the two major known titanium resources in Iran. The main host rocks of the ore body are ultramafics including wehrlite and lherzolite with minor clinopyroxenite. Qara Aqaj intrusion is composed mainly of ultramafic-mafic rocks, layered gabbro, diorite, microdiorite and some monzonite and alkali syenite. This intrusion has intruded the basement complex (amphibolite schist and gneiss), and it is covered unconformably by upper Permian sandstone and limestone. Therefore the age of intrusion can possibly be pre upper Permian. Based on structural and geochemical characteristics, Qara Aqaj intrusion can be divided into basal and main zones. The basal zone is composed of fine grain gabbro with weak layering and alteration, probably originated from a primary tholeiitic magma. This zone is enriched in Si, Na, Mg and Cr and poor in Fe, Ti and P relative to the main zone. Due to low oxygen fugacity (ƒO2) Fe-Ti minerals are not crystallized in the basal zone. It seems that the main zone that forms the main body of the Qara Aqaj intrusion is injected into the tholeiitic magma. Based on the results from drilling four ore bearing wehrlite layers varying in thickness from 1.5 m to 22 m with 33.5 m maximum combined thickness are recognized. Gabbro layers that are in contact with ultramafic layers have no economic mineralization. Some uneconomic oxide minerals are found as inclusions in silicate minerals, or open space fillings. Ore minerals in the ultramafic rocks cropping out in the study area include (in average) 10.58% wt ilmenite, 9.21% wt Ti bearing magnetite, 6.09% wt magnetite and 3.46% wt apatite (fluorapatite). The ore minerals in core samples are as follows (in average): 8.93% wt ilmenite, 8.27% wt Ti bearing magnetite, 5.52% wt magnetite and 4.25% wt apatite. The weight ratio of Fe-Ti oxide minerals to apatite varies from 4 to 30 (average 8). Qara Aqaj titanium potential can be considered as a large titanium bearing orebody. It is similar to the low grade apatite-ilmenite-magnetite deposit in the Kauhajarvi gabbro in western Finland.