The use of asphaltic crude oil resources as an alternative to offset light oil supplies over the next years has attracted oil field attention. However, its high viscosity greatly impedes the production of asphaltic crude oil from wells and constitutes an obstacle, especially during transportation and refining operations. Thus, catalytic aquathermolysis has been introduced as an attractive and green technique for upgrading the asphaltic crude oil at elevated temperatures by reducing the asphaltic crude oil viscosity. In this study, magnetic multiwalled carbon nanotubes (MWCNTs) were prepared and modified with 1-ethyl-3-(3-formyl-4-hydroxybenzyl)-1H-imidazol-3-ium acetate (EFHIA). The results revealed the rheology results revealed that the viscosity of crude oil was reduced by 75.9% when compared to thermally treated blank at the same degree after 2 h of operation using Fe3O4/MWCNT@EFHIA as a catalyst. The asphaltene, resin, and sulfur measurements revealed that the percentages of these compounds were reduced to 37%, 43%, and 47%, respectively, upon using 0.2% Fe3O4/MWCNT@EFHIA as a catalyst at 200 degrees C for 2 h.