A Ni-based single crystal superalloy according to the invention has, for example, a composition including: 5.0 to 7.0 wt % of Al, 4.0 to 10.0 wt % of Ta, 1.1 to 4.5 wt % of Mo, 4.0 to 10.0 wt % of W, 3.1 to 8.0 wt % of Re, 0.0 to 2.0 wt % of Hf, 2.5 to 8.5 wt % of Cr, 0.0 to 9.9 wt % of Co, 0.0 to 4.0 wt % of Nb, and 1.0 to 14.0 wt % of Ru in terms of weight ratio; and the remainder including Ni and incidental impurities. In addition, the contents of Cr, Hf and Al are preferably set so as to satisfy the equation OP≧108. According to the Ni-based single crystal superalloy of the invention, high creep strength can be maintained and the oxidation resistance can be improved.