High-precision mass measurements of a pentaquark (5Q) Θ+ in the JP=3/2± channels are performed in anisotropic quenched lattice QCD. A large number of gauge configurations (Nconf=1000) are prepared for the standard Wilson gauge action at β=5.75 and the O(a) improved Wilson (clover) quark action is employed for κ=0.1210(0.0010)0.1240 on a 123×96 lattice with the renormalized anisotropy as as/at=4. The Rarita-Schwinger formalism is adopted for interpolating fields. We examine several interpolating fields with isospin I=0, such as (a) the NK*-type, (b) the color-twisted NK*-type, and (c) the diquark-type operators. After chiral extrapolation, we obtain massive states, m5Q 2.1-2.2GeV in JP=3/2-, and m5Q=2.4-2.6GeV in JP=3/2+. Analyses using the hybrid boundary condition method are performed to determine whether these states are compact 5Q resonances or two-hadron scattering states. No compact 5Q resonance state is found below 2.1 GeV. © 2005 The American Physical Society.