The spawning relationships with temperature/photoperiod of Strombus gigas were investigated considering three habitats in Alacranes Reef, Yucatan, between February 1999 and March 2000. The sites were 22 degrees 34'N, 89 degrees 42'W (site 1); 22 degrees 29'N, 89"45'W (site 2) and 22 degrees 22'N, 89 degrees 39'W (site 3). At each site, transects (100 m x 10 m) were done. Different kinds of reproductive behavior of S. gigas was observed: such as copulating and egg-laying. Individuals alone and egg masses were registered as well. The S. gigas shell length and lip thickness were measured. High density of adults was found at site 2 with 87 conchs in one transect of 1000 m2. The mean density per m2 was 0.004 for site 1; 0.035 for site 2; and 0.003 for site 3. The mean shell length was 220 mm and the lip thickness mean was 16 mm (N = 783) for all sites. In February 1999 egg-laying female was found on sand. There was a high reproductive activity at site 2 with 8 egg-laying and 18 egg masses. Minimum reproductive activity was found at site 3 with 2 egg masses. The bottom-water temperature was related positively with copulating pairs (r = 0.723, f = 11.05, p < 0.01) and egg masses (r = 0.736, f = 11.82, p < 0.1). Correlation between photoperiod with copulating pairs (r = 0.857, f = 27.78, p < 0.01) and egg masses (r = 0.782, f = 15.77, p < 0.01) were found as well.