An exhaust gas purification system for an internal combustion engine comprising: a pre-catalyst that is arranged in an exhaust passage of the internal combustion engine and has an oxidation function; a fuel supply device configured to supply fuel to said pre-catalyst; a filter that is arranged in the exhaust passage at a location downstream of said pre-catalyst for trapping particulate matter in exhaust gas, and supports thereon an NOx selective reduction catalyst which serves to reduce NOx in the exhaust gas by using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or a precursor of ammonia to said filter; a post-catalyst that is arranged in the exhaust passage at a location downstreamof said filter, and has an oxidation function; and a filter regeneration processing execution unit configured to carry out filter regeneration processing in which fuel is supplied from said fuel supply device to said pre-catalyst thereby to raise the temperature of said filter to a predetermined filter regeneration temperature at which oxidation of the particulate matter is promoted, whereby the particulate matter deposited in said filter is oxidized and removed; characterized in that the filter regeneration processing execution unit is configured to, when the temperature of said post-catalyst is lower than a predetermined activation temperature at the time the execution of said filter regeneration processing is requested, raise the temperature of said post-catalyst to a temperature equal to or higher than said predetermined activation temperature by carrying out control of raising the temperature of the exhaust gas discharged from the internal combustion engine and control of increasing the flow rate of the exhaust gas, before the execution of said filter regeneration processing by said filter regeneration processing execution unit. a pre-catalyst that is arranged in an exhaust passage of the internal combustion engine and has an oxidation function; a fuel supply device configured to supply fuel to said pre-catalyst; a filter that is arranged in the exhaust passage at a location downstream of said pre-catalyst for trapping particulate matter in exhaust gas, and supports thereon an NOx selective reduction catalyst which serves to reduce NOx in the exhaust gas by using ammonia as a reducing agent; an ammonia supply device configured to supply ammonia or a precursor of ammonia to said filter; a post-catalyst that is arranged in the exhaust passage at a location downstreamof said filter, and has an oxidation function; and a filter regeneration processing execution unit configured to carry out filter regeneration processing in which fuel is supplied from said fuel supply device to said pre-catalyst thereby to raise the temperature of said filter to a predetermined filter regeneration temperature at which oxidation of the particulate matter is promoted, whereby the particulate matter deposited in said filter is oxidized and removed; characterized in that the filter regeneration processing execution unit is configured to, when the temperature of said post-catalyst is lower than a predetermined activation temperature at the time the execution of said filter regeneration processing is requested, raise the temperature of said post-catalyst to a temperature equal to or higher than said predetermined activation temperature by carrying out control of raising the temperature of the exhaust gas discharged from the internal combustion engine and control of increasing the flow rate of the exhaust gas, before the execution of said filter regeneration processing by said filter regeneration processing execution unit.