This work targets the preparation and characterization of an inexpensive TiO₂-fly ash composite membrane for oily wastewater treatment. The composite membrane was fabricated by depositing a hydrophilic TiO₂ layer on a fly ash membrane via the hydrothermal method, and its structural, morphological and mechanical properties were evaluated. The separation potential of the composite membrane was evaluated for 100–200 mg·L^–1 synthetic oily wastewater solutions. The results show that the composite membrane has excellent separation performance and can provide permeate stream with oil concentration of only 0.26–5.83 mg·L^–1. Compared with the fly ash membrane in the average permeate flux and performance index (49.97 × 10^–4 m³·m^–2·s^–1 and 0.4620%, respectively), the composite membrane exhibits better performance (51.63 × 10⁻⁴ m³·m⁻²·s⁻¹ and 0.4974%). For the composite ash membrane, the response surface methodology based analysis inferred that the optimum process parameters to achieve maximum membrane flux and rejection are 207 kPa, 200 mg·L^–1 and 0.1769 m·s^–1 for applied pressure, feed concentration and cross flow velocity, respectively. Under these conditions, predicted responses are 41.33 × 10^–4 m³·m⁻²·s⁻¹ permeate flux and 98.7% rejection, which are in good agreement with the values obtained from experimental investigations (42.84 × 10⁻⁴ m³·m⁻²·s⁻¹ and 98.82%). Therefore, we have demonstrated that the TiO₂-fly ash composite membrane as value added product is an efficient way to recycle fly ash and thus mitigate environmental hazards associated with the disposal of oily wastewaters.