Biofouling organisms attached on mariculture cages were studied inDaya Bay, Guangdong province in 1986 to 1987. 124 species of organisms wererecorded. The dominant species were Mycale adhaereris, Bugula neritina, Schizopo-rella unicornis, Hydroides elegans, Ostrea radix, Balanus reticulatus, Styela plicataand S. canopus. These organisms grew throughout the year, and the most flourishperiod was from March to June. The wet weights attached organisms on mariculturecages were 8.3-545.0g/m² monthly and 150.0-6250.5g/m² seasonally. The great-est cover areas were 73.4% monthly and 94.9% seasonally. The biofouling onpearlshell cages was more flourish in summer than in winter. The greatest record-ed wet weight was 4506.2g/m² on pearlshell cages. In summer, the number of bio-fouling species on pearlshell reached as many as 50 species, when the wet weightreached as high as 16.5 of each pearlshell.