Pretreatment of biomass with phosphoric acid (H3PO4) has been a popular method since it facilitates the generation of biofuels and mitigates the problems arising from the use of corrosive sulfuric acid that is otherwise commonly employed for pretreatment. However, variations took place in the structure of biomass through this treatment have not so far been investigated in detail. This paper focuses on the effects of aqueous H3PO4 treatment on the lignocellulosic residue of corn (CR) considering the fuel properties, ash fusion temperatures, combustion characteristics and kinetics, mineral phases, surface functionalities, and the morphology of the treated biomass. It was determined that interaction of biomass with 5% H3PO4 solution led to important variations from cellulose crystallinity to thermal reactivity of this lignocellulosic material. Although elements such as Na, K, Ca, Mg, and Fe could be effectively removed by treatment, formation of phosphorus containing new phases caused to increase in ash yield. Also, the change in mineral matter composition led to an increase in ash fusion temperatures along with reduction in the burning rates. Thus, the combustibility and combustion performance indices dropped.