Abstract We report a measurement of the electric dipole moment of the τ lepton (dτ) using an 833 fb −1 data sample collected near the Υ(4S) resonance, with the Belle detector at the KEKB asymmetric-energy e + e − collider. Using an optimal observable method, we obtain the real and imaginary parts of d τ as Re(d τ ) = (−0.62 ± 0.63) × 10 −17 ecm and Im(d τ ) = (−0.40 ± 0.32) × 10 −17 ecm, respectively. These results are consistent with null electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.