An exhaust gas purification system for an engine having a combustion chamber, the exhaust gas purification system comprising: an exhaust passage extending from the combustion chamber of the engine; and upstream and downstream exhaust purifying units (10, 11) disposed in the exhaust passage and configured to purify exhaust gas in the exhaust passage, wherein the upstream exhaust purifying unit is disposed upstream of, and in juxtaposition with, the downstream exhaust purifying unit along an exhaust gas flow direction in the exhaust passage, and includes a first purifier comprising a three-way catalyst layer as a nitrogen oxide reduction element having a function of reducing nitrogen oxides in the exhaust gas, and wherein the downstream exhaust purifying unit includes: a first purifier comprising a three-way catalyst layer having at least a function of oxidizing components in the exhaust gas, the first purifier covering, as an underlayer, an outer surface of a carrier disposed in the exhaust passage; and a second purifier having a function of purifying the exhaust gas by reducing, using occluded ammonia, the components in the exhaust gas that have been oxidized in the first purifier, the second purifier including a superposed portion covering, as an upper layer, an entire length of an outer surface of the first purifier, and an unsuperposed portion located downstream of the first purifier and covering the outer surface of the carrier. an exhaust passage extending from the combustion chamber of the engine; and upstream and downstream exhaust purifying units (10, 11) disposed in the exhaust passage and configured to purify exhaust gas in the exhaust passage, wherein the upstream exhaust purifying unit is disposed upstream of, and in juxtaposition with, the downstream exhaust purifying unit along an exhaust gas flow direction in the exhaust passage, and includes a first purifier comprising a three-way catalyst layer as a nitrogen oxide reduction element having a function of reducing nitrogen oxides in the exhaust gas, and wherein the downstream exhaust purifying unit includes: a first purifier comprising a three-way catalyst layer having at least a function of oxidizing components in the exhaust gas, the first purifier covering, as an underlayer, an outer surface of a carrier disposed in the exhaust passage; and a second purifier having a function of purifying the exhaust gas by reducing, using occluded ammonia, the components in the exhaust gas that have been oxidized in the first purifier, the second purifier including a superposed portion covering, as an upper layer, an entire length of an outer surface of the first purifier, and an unsuperposed portion located downstream of the first purifier and covering the outer surface of the carrier. a first purifier comprising a three-way catalyst layer having at least a function of oxidizing components in the exhaust gas, the first purifier covering, as an underlayer, an outer surface of a carrier disposed in the exhaust passage; and a second purifier having a function of purifying the exhaust gas by reducing, using occluded ammonia, the components in the exhaust gas that have been oxidized in the first purifier, the second purifier including a superposed portion covering, as an upper layer, an entire length of an outer surface of the first purifier, and an unsuperposed portion located downstream of the first purifier and covering the outer surface of the carrier.