High-quality ultrathin single-crystalline SnSe2 flakes are synthesized under atmospheric-pressure chemical vapor deposition for the first time. A high-performance photodetector based on the individual SnSe2 flake demonstrates a high photoresponsivity of 1.1 x 10(3) A W-1, a high EQE of 2.61 x 10(5)%, and superb detectivity of 1.01 x 10(10) Jones, combined with fast rise and decay times of 14.5 and 8.1 ms, respectively.