We have searched for the lepton flavor violating decays τ- → ℓ- KS 0 (ℓ = e or μ), using a data sample of 281 fb-1 collected with the Belle detector at the KEKB e+ e- asymmetric-energy collider. No evidence for a signal was found in either of the decay modes, and we set the following upper limits for the branching fractions: B (τ- → e- KS 0) < 5.6 × 10-8 and B (τ- → μ- KS 0) < 4.9 × 10-8 at the 90% confidence level. These results improve the previously published limits set by the CLEO Collaboration by factors of 16 and 19, respectively. © 2006 Elsevier B.V. All rights reserved.