We have investigated the effect of oxygen precipitates on dislocation motion in Czochralski silicon by the indentation technique. It is found that the gliding distances of dislocations are much smaller in samples containing a high density of oxygen precipitates in the order of 109 cm-3 than in the control samples without remarkable oxygen precipitates. Transmission electron microscopy reveals that oxygen precipitates can indeed pin the dislocations generated at high temperatures. Such a pinning effect is proved to be dependent on the density and size of oxygen precipitates. The particle strengthening mechanism is tentatively adopted to explain the suppression of dislocation motion by the oxygen precipitates in CZ silicon.