To provide a highly detailed ink jet recording sheet realizing a variable dot diameter and an ink jet recording system.

This ink jet recording sheet is constituted by providing an undercoat layer composed of a polymer gel having a lower limit critical eutectic temp. of 50°C or higher between a support and an ink receiving layer or adding a polymer gel to the ink receiving layer or providing an overcoat layer composed of the polymer gel on the ink receiving layer or by mixing an ink absorbable polymer having no lower limit critical eutectic temp. and the polymer gel to provide the ink receiving layer having an island structure. Further, the arbitrary region of the recording sheet is heated to a specific temp. or higher.