Maya crude was hydrotreated in a pilot plant at different reaction conditions such as temperatures of 380420 degrees C, pressures of 70-100 kg/cm(2), and LHSVs of 0.33-1.5 h(-1). Asphaltenes were precipitated with n-heptane from each hydrotreated product and thereafter fractionated by using a mixture of solvents. A pressurized system was used to precipitate asphaltenes at 25 kg/cm(2) N-2 and 60 degrees C with a n-heptane/hydrotreated crude ratio of 5: 1. Three fractions were obtained and characterized by elemental analysis, metal content (Ni and V), and MALDI mass spectra to obtain molecular weight distributions. Reaction conditions during hydrotreating of Maya crude influenced the asphaltene properties in different ways which became evident with the fractionation. Fractionation allowed asphaltene molecules to be separated according to their solubility properties. Additionally, asphaltenes were fractionated taking into account their molecular weight distribution obtained by size exclusion chromatography (SEC) with tetrahydrofuran as solvent. Asphaltenes were divided into three fractions of molecular weight, and a possible mechanism of how molecular weight. is distributed on each fraction of asphaltenes was proposed.