Codium fragile (Suringar) Hariot, an edible green alga is farmed in Korea by natural blooming zygotes attachment. Experiments were conducted to reveal the conditions for artificial seed production of C. fragile by sexual and asexual reproduction. Growth was compared between zygotes attachment (sexual reproduction) and isolated utricles with medullary filaments (asexual reproduction). Zygotes and isolated utricles with medullary filaments were cultured under different light conditions (10, 20, 40, 60 and $100;{mu}mol{cdot}m^{-2}{cdot}s^{-1}$) and temperatures (5, 10, 15, 20 and $25^{circ}C$) under 16:8LD. Maximum growth of zygote was $261.3{pm}21.0;{mu}m$ under $15^{circ}C$ and $20;{mu}mol{cdot}m^{-2}{cdot}s^{-1}$ after 13 days culture. Maximum regeneration of isolated medullary filament was $8.1{pm}1.7;mm$ per one isolated utricle under $20^{circ}C$ and $100;{mu}mol{cdot}m^{-2}{cdot}s^{-1}$ after 15 days culture. After intermediate culture during two months in the field, morphogenesis occurred in both sexual and asexual reproduction, and growth of young thalli was not significantly different (p>0.05) between the both reproduction methods. Even though seed production of C. fragile is possible in both sexual and asexual reproduction, the mass artificial seed production of asexual reproduction is much more effective than that of sexual reproduction that is too much affected by maturity.