Condensed and low-defected graphitic carbon nitride (denoted as CNa) was synthesized from a simple one-step thermal polymerization in ammonia. The promotion effect in the structural evolution during condensation in ammonia and catalytic performance for H-2 evolution for the defected-C3N4 was well studied. Comparing to pristine g-C3N4 prepared from polymerization in nitrogen (CNn), the as-prepared sample has the same composition and graphitic stacking structure, but appears well dispersed flake morphology with larger surface area and more mesoporous texture. Surprisingly, this sample possessed much condensed crystallinity and improved in-plane conjugated network with decreased sp(2) N defects in heptazine heterocycle. Consequently, higher rate of photocatalytic H-2 production under visible light irradiation, about 6 times of CNn, was achieved, owing to the broader distribution of active sites and more efficient transport and separation of photogenerated charge carriers in the improved ordered skeleton microstructure. (C) 2015 Elsevier B.V. All rights reserved.