We report the discovery of bulk superconductivity (SC) at 6.1 K in a quasi-one-dimensional chromium pnictide K2Cr3As3 that contains (Cr3As3)2−∞ double-walled subnanotubes with face-sharing Cr6/2 (As6/2 ) octahedron linear chains in the inner (outer) wall. The material has a large electronic specific-heat coefficient of 70–75mJK−2mol−1 , indicating significantly strong electron correlations. A linear temperature dependence of resistivity in a broad temperature range from 7 to 300 K is observed, which suggests non-Fermi liquid behavior of the material. Unconventional SC is preliminarily manifested by the estimated upper critical field exceeding the Pauli limit by a factor of 3–4. The title compound represents a rare example that possibly unconventional SC emerges in a quasi-1D system with strong electron correlations.