For a successful implementation of the oxy-fuel combustion technology, a good understanding of ash-related issues has to be achieved. Knowledge is still lacking on how oxy-fuel combustion can affect ash properties and its sintering behavior. These are the focus of the present work. Combustion experiments of a sub-bituminous coal were carried out in a drop tube furnace at 1573 K and under air and different oxy-fuel conditions (i.e., OXY21, 21 vol % O-2/79 vol % CO2; OXY27, 27 vol % O-2/73 vol % CO2; and OXY32, 32 vol % O-2/68 vol % CO2). The bulk ash samples were collected and subjected to analyses by techniques such as computer-controlled scanning electron microscopy, X-ray diffraction, and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Sintering tests of the bulk ashes were performed at temperatures ranging from 1023 to 1223 K. The compressive strength of sintered ash was characterized. The results show that oxy-fuel combustion has significant impacts on ash speciation rather than its elemental composition. Ash particle size distributions are also affected, which is mainly attributed to changes in char burning temperatures. Oxy-fuel combustion seems to have insignificant effects on the temperature at which the ash pellet starts to sinter but apparently affects the ash sintering strength. In comparison to the ash from air combustion (AIR ash), the OXY21 ash has a much higher sintering strength. Nevertheless, a decrease of the sintering strength is observed for the OXY27 and OXY32 ashes compared to the OXY21 ash. Such differences are attributed to changes in ash chemical properties.