The present invention aims to provide a method for producing a porous substrate containing a bioabsorbable polymer and heparin in a simple manner without use of a surfactant, a porous substrate containing a bioabsorbable polymer and heparin, and an artificial blood vessel. The present invention provides a method for producing a porous substrate containing a bioabsorbable polymer and heparin, including: a solution preparing step of preparing a heparin-bioabsorbable polymer solution having heparin uniformly dispersed therein and a bioabsorbable polymer dissolved therein, using the bioabsorbable polymer, the heparin, a solvent 1 that is a poor solvent having a lower solvency for the bioabsorbable polymer, a solvent 2 that is a good solvent having a higher solvency for the bioabsorbable polymer and is incompatible with the solvent 1, and a common solvent 3 compatible with the solvent 1 and the solvent 2; a precipitating step of cooling the heparin-bioabsorbable polymer solution to precipitate a porous body containing the bioabsorbable polymer and the heparin; and a freeze-drying step of freeze-drying the porous body containing the bioabsorbable polymer and the heparin to provide a porous substrate containing the heparin.