Seedlings of Morus alba were grown in different sex cultivation modes (female-female, F-F; male-male, M-M; female-male, F-M) to evaluate their biomass and allocation. The results showed that the total biomass of M. alba in modes F-F and F-M were higher than in M-M, with increments of 31.6% and 39.2%, respectively. The leaf biomass of M-M was lower than that of F-F (-41.7%), while the root biomass of F-M was higher than that of F-F (+34.5%). Root biomass fraction and root to shoot ratio of F-M were the highest among the three cultivation modes. Our results indicated that the biomass of M. alba was related to the sexrelated cultivation mode, with the highest in F-M and the lowest in M-M among the three treatments.