The effect of season, life stages and harvesting sites on the yield and properties of agars extracted from Gracifaria verrucosa were determined. G. verrucosa were collected seasonally from November 2001 to August 2002 at Cheongsapo and Boryong, Korea. The plants were sorted into the different life stages (tetrasporophytes and gametophytes) and dried at 60℃ . The yield, sulfate, protein, uronic acid and 3,6-anhydrogalactose of the agar were determined, and standard parameters of physical quality were measured. No differences were found in yield and properties of agars from the two different harvesting sites and from life history phases. The yield of agar was maximum in summer (17.3-20.0%) and minimum in winter (11.9-13.1%). Maximum gel strength occurred in winter when the agar yield and sulfate content were low. Gel strength was negatively correlated with agar yield. Seasonal variations in agar yield and its quality were discussed in a view to managing the exploitation of this resource.