Ba 3IrTi 2O 9 crystallizes in a hexagonal structure consisting of a layered triangular arrangement of Ir4 +(J eff=12). Magnetic susceptibility and heat capacity data show no magnetic ordering down to 0.35 K in spite of a strong magnetic coupling as evidenced by a large Curie-Weiss temperature θ CW∼-130 K. The magnetic heat capacity follows a power law at low temperature. Our measurements suggest that Ba 3IrTi 2O 9 is a 5d, Ir-based (J eff=12), quantum spin liquid on a two-dimensional (2D) triangular lattice. © 2012 American Physical Society.