PrV2Al20 is a rare example of a heavy fermion system based on strong hybridization between conduction electrons and nonmagnetic quadrupolar moments of the cubic Γ3 ground doublet. Here, we report that a high-quality single crystal of PrV2Al20 exhibits superconductivity at Tc = 50 mK in the antiferroquadrupole-ordered state under ambient pressure. The heavy fermion character of the superconductivity is evident from the specific heat jump of ∆C/T ∼ 0.3 J/mol K 2 and the effective mass m * /m0 ∼ 140 estimated from the temperature dependence of the upper critical field. Furthermore, the high-quality single crystals exhibit double transitions at TQ = 0.75 K and T * = 0.65 K associated with quadrupole and octapole degrees of freedom of the Γ3 doublet. In the ordered state, the specific heat C/T shows a T 3 dependence, indicating the gapless mode associated with the quadrupole and/or octapole order. The strong sensitivity to impurity of the superconductivity suggests unconventional character due to significant quadrupolar fluctuations.PACS numbers: 74.70. Tx, 75.25.Dk, 72.15.Qm 4f electron systems exhibit a large variety of nontrivial ground states by tuning the hybridization between localized 4f and conduction (c−) electrons. Especially, emergence of exotic superconductivity (SC) with a large effective mass from unconventional quantum criticality has attracted much attention [1][2][3][4][5]. While most of the examples have been reported at the border of magnetism [6,7], similarly exotic states of matter may be found in the vicinity of quantum phase transition associated with different degrees of freedom of f -electrons, such as electrical quadrupole (orbital) and valence. In particular, experimental exploration of the quadrupolar instability is important since few studies on the associated quantum criticality has been made to date.For the exploration, the simplest example could be found in materials that carry no magnetic but quadrupole moments. Such a nonmagnetic ground state is known as the Γ 3 doublet in the cubic crystalline electric field (CEF) of a f 2 configuration. Intensive studies have revealed various interesting states in the cubic Γ 3 doublet systems, in particular in Pr-based intermetallic compounds [8][9][10][11][12]. However, Pr-based cubic Γ 3 doublet systems usually have well-localized quadrupole moments, and thus until quite recently there have been no study on the quadrupolar instability by tuning the c-f hybridization.PrT r 2 Al 20 (T r = Ti, V) has been reported as a rare example of cubic Γ 3 -doublet based Kondo lattice systems where one may tune the hybridization strength between quadrupole moments and conduction electrons by chemical substitution and by pressure [13,14]. These materials have the nonmagnetic Γ 3 CEF ground state with the well separated excited state at ∆ CEF ∼ 60 K (Ti) and 40 K (V), as confirmed by various experiments [13,15,16], and * Electronic address: satoru@issp.u-tokyo.ac.jp exhibit the respective ferro-and antiferro-quadrupole ordering at T Q = 2.0 K (Ti) and 0.6 K (...