In this work, NiFe nanocatalysts with di fferent molar ratios 1:0.33, 1:1 and 1:3 were synthesized by a modi fied inverse microemulsion method at Soft Chemistry conditions in order to apply them to heavy crude oil (HCO) in situ hydroprocessing and to improve their physico-chemical properties. All samples were characterized by mean, atomic absorption (AA), small -angle X-ray scattering (SAXS), scanning transmission electron microscopy (STEM), X-ray energy dispersion spectroscopy (EDX), and X-ray photoelectron emission spectroscopy (XPS). Catalytic evaluation of nanocatalysts was performed in a batch reactor at 372 ?C, 9.8 MPa of initial H 2 pressure and 1 h of reaction time. The reaction products, were analyzed by means analysis of saturates, aromatics, resins, and asphaltenes (SARA) fractions, simulated distillation (SIMDIS), API gravity, rheology, and nitrogen and sulfur contents. Techniques applied reveal that nanoparticles of NiFe with spherical morphology with average sizes in the range (1 -20) nm and agglomerates smaller than 50 nm were obtained. The nanocatalysts synthesized im- proved API gravity from 13.1 to 18.3, furthermore, the asphaltenes conversion was into 37.2 -43.7%. Moderate sulfur and nitrogen removal was obtained. SARA analysis indicated that saturated and aromatics fractions in- creased while resins and asphaltenes were reduced.