An array of Fe2O3/g-C3N4 nanocomposites was fabricated via an in situ pyrolysis procedure. The samples’ structural, optical, and morphological characteristics were investigated. All the α-Fe2O3/g-C3N4 nanocomposites exhibit a rhombohedral phase of α-Fe2O3 besides the g-C3N4 phase. The FTIR studies corroborate the sp2-hybridized C and N bonds in g-C3N4 as well as Fe–O stretching vibrations in the α-Fe2O3/g-C3N4 nanocomposites. From the SEM study, the g-C3N4 nanoflakes are attached to crystals of α-Fe2O3, with a distinct interface forming between them. The chemical bonding states of the constituent elements are revealed by the XPS analysis performed on the 0.5α-Fe2O3/g-C3N4 nanocomposite. The photoluminescence investigations exhibit that the hybridization of α-Fe2O3 and g-C3N4 is successful in separating photoinduced charge carriers. The photocatalytic efficacy of the nanocomposites was investigated by degrading methylene blue under visible light irradiation. After 75 min of irradiation, the 0.5α-Fe2O3/g-C3N4 nanocomposite demonstrated a remarkable photocatalytic degradation efficiency of 89%