Graphitic carbon nitride (g-C₃N₄), agreen and efficient heterogeneous photocatalyst, wasapplied for photo-atom transfer radical polymerization (photo-ATRP) without any additives. The polymerization was instantly switched on and off by a blue LED. The polymer molecular weights and their distributions were controlled for methacrylate monomers up to fairly high conversions in many cases. The block copolymers were also obtained to demonstrate good end-group fidelity. Moreover, this g-C₃N₄ catalyzed photo-ATRP could be carried out in the presence of oxygen which implied good oxygen-tolerance. The catalytic efficiency of g-C₃N₄ almost did not reduce after photo-ATRP recycling seven times. Facile operation, oxygen tolerance and sustainability are advantages of this g-C₃N₄ catalyzed photo-ATRP.