The effects of blending and heat-treating of two atmospheric residues (ARs) from Lower Fars crude and Kuwait export crude on the distribution and composition of their saturate, aromatic, resin, and asphaltene (SARA) fractions were studied using X-ray diffraction (XRD), high-temperature gas chromatography equipped with an atomic emission detector (HT-GC-AED), gel permeation chromatography with detection by ultraviolet absorbance (GPC-UV), and inductively coupled plasma mass spectrometry (GPC-ICP-MS). Although no obvious change in the mass distribution of the SARA fractions is observed, the result from the GPC-ICP-MS analysis shows that blending of the two ARs at room. temperature causes the shift of the metal complexes from the asphaltenes to the resins. Heat-treating of the ARs at 330 degrees C for 3 h under an H-2 pressure of 9 MPa changes the mass distribution of the SARA fractions and promotes the shifts of V and Ni complexes in the asphaltenes from the heavy molecular weight to the light molecular weight and further from the asphaltenes to the resins. The results suggest some potential approaches for improving the hydrodemetallization reactivity of AR by releasing the metals complexes from the asphaltenes.