The experiment is conducted on the effects of the difference densities and time spans of photosynthet ic bacteria liquor soaked with Laminaria japonica and Gracilaria sp. on the growth of two different sizes of Haliotis diversicolor aquatilis . The result shows that the effects of photosynthetic bacteria on the growth vary w ith different densities and time spans of photosynthetic bacteria liquor soaked with Laminaria japonica and Gracilaria sp. . The greater the density and the longer the soaking time the more apparent the effect is on the growth of Haliotis diversicolor aquatilis. The average growth rates of the shell of Haliotis diversicolor aquatilis in the experimental groups w ith 150 @ 10- 6( V/ V) and 3-4h or 200 @ 10-6 ( V/ V) and 2-3h of photosynthetic bacteria liquor soaked w ith Laminaria japonica and Gracilaria sp. is at least 5% higher than that of the control group. The largest one can be 11. 5% higher ( P< 0. 05) .