Abstract: This study evaluates the fuel quality and thermochemical suitability of sewage sludge (SS), municipal solid waste (MSW), and selected SS–MSW blend ratios for co-pyrolysis applications. Proximate and ultimate analyses were used to assess the compositional behavior of the feedstocks, with particular attention to fixed carbon, volatile matter, nitrogen, sulfur, ash, moisture, elemental ratios, and higher heating value (HHV). The results show that MSW possesses superior fuel characteristics relative to SS, with higher volatile matter(83.70%), higher fixed carbon(7.50%), lower ash(0.45%), lower nitrogen(0.64%), and higher HHV(18.91KJ/Kg). In contrast, sewage sludge is characterized by very high ash content(42%) and elevated nitrogen(2.71%), indicating a mineral-rich and heteroatom-laden feedstock with lower thermal efficiency and greater environmental control requirements.The blended feedstocks exhibited a strong non-linear response to increasing SS fraction. Ash content increased sharply with sludge addition, while HHV declined progressively, confirming that even moderate sludge incorporation substantially alters the thermal behavior of the mixture. The observed trends suggest that SS dominates the inorganic residue profile and depresses the energy density of the blend, whereas MSW contributes more favorable volatile and combustible fractions. These findings indicate that co-pyrolysis performance is highly composition-dependent and that feedstock selection must balance energy recovery potential against ash-related operational constraints.