Lilium Oriental hybrid ‘Sorbonne’ were cultured in vitro for 49 days on Murashige and Skoog (MS) medium containing 0, 30, 60, 90, 120 g l^-1 sucrose respectively (i.e. S₀, S₃₀, S₆₀, S₉₀ and S₁₂₀ treatments) under heterotrophic and continuous dark conditions. The results showed that an increase in sucrose concentration in the medium from S₀ to S₉₀ improved the bulblet growth, and associated with an increase in the ratio of dry weight to fresh weight of bulblet. The S₉₀ bulblets had greatest fresh and dry weight, and perimeter. Total sugar content of bulblet increased with increasing sucrose concentration from S₀ to S₉₀ and culture time. The uptake carbon by bulblets from medium also increased with increasing sucrose concentration in the medium from S₀ to S₉₀; however, about 54% to 67% of the uptake carbon had been consumed for dark-respiration. The carbon loss due to autoclaving was 10.8% to 12.4% of the total carbon in the medium, and residual carbon in the medium, which was 11.2% to 39.8%, increased with increasing sucrose concentration. The absence of sugar in the medium not only had no carbon accumulation but also decreased the original carbon of bulblets. Carbon balance of lily bulblets was affected by initial sucrose concentration of the medium. In the S₉₀ treatment, 30% of total carbon was fixed in bulblet, 35% consumed for dark-respiration, 10.8% lost due to autoclaving, and 24.2% resided in the medium at the end culture. The results indicated that sucrose concentration of 60 to 90 g l^-1 was more suitable for growth of lily bulblets under heterotrophic conditions with continuous dark due to better growth, higher carbohydrate accumulation, and reasonable carbon balance.