This study evaluates the effect of weekly immersion baths in fresh water and a 0.2% solution of calcium hydroxide (lime) on the intensity of fouling polychaete worms in Crassostrea gigas oysters. Initially, 135 juvenile oysters (with an average length of 2.75 ± 0.25 cm and a mean wet weight of 4.33 ± 0.96 g) were randomly assigned to three groups with three replicates each. Two groups were treated for 10 minutes with lime and fresh water, respectively, and a third group remained as control. Fouling polychaete intensity and the bivalve length and weight were obtained every 15 days. Every week oyster survival was registered for each treatment and water parameters were measured at the culture site. Significant differences (P < 0.05) in worm intensity were found between the two bath treatments and the control. The lime treatment showed the lowest intensity (number of mud tubes/oyster) in all the sampling days, with no increase in intensity during the last experimental month. There were no significant differences (P > 0.05) in final survival, final length, final weight and final condition index of the oysters among treatments after 112 days of study.