An exhaust gas conversion system includes an oxide catalyst, a filter, a selective catalytic reduction catalyst and an ammonia supplying device. The filter has a honeycomb structural body including a honeycomb unit. The selective catalytic reduction catalyst has a honeycomb structural body including a honeycomb unit. The oxide catalyst, the filter and the selective catalytic reduction catalyst are sequentially arranged in a direction in which an exhaust gas flows. A ratio of an area of a cross section of the selective catalytic reduction catalyst perpendicular to a longitudinal direction of the selective catalytic reduction catalyst with respect to an area of a cross section of the filter perpendicular to a longitudinal direction of the filter is approximately 0.55 or more and approximately 0.90 or less. The area of the cross section of the filter is approximately 300 cm2 or more and approximately 1000 cm2 or less.