In an experiment at Fermilab we have measured the lifetime of KS0 mesons produced by 800-GeV/c protons on tungsten. KS0+- decays from 100 to 350 GeV/c, between 9.3 and 25.3 m from production, were selected for the measurement. The result was (0.8920 0.0044)×10-10 sec, in excellent agreement with measurements performed for 25-GeV/c KS0. The lifetime was also calculated for seven momentum bins. The results were completely consistent with Lorentz invariance. No evidence was found for the mometnum dependence suggested by the intermediate-range fifth-force hypothesis.