A high yield of beta-carotene, 48 mg/l, was obtained by cultivation of a strain of Blakeslea trispora under a strong alkaline culture condition (pH 10), which was significantly higher than those obtained under milder pH conditions (3.26 - 7.80 mg/l at pH 4 to 8). The formation of small pellets at pH 10 was observed, whereas a single large cluster was formed for the pHs ranged from 4 to 8. Span 20 at 0.1 to 1% in the culture medium changed cellular morphology to micro-pellets regardless of the culture pH. The same trend of beta-carotene production, depending on the alkalinity of the culture broth, was also observed in the presence of 1% of Span 20 yielding much higher productivity. The amounts of beta-carotene yielded at pH 10 and 11 were 92.0 and 100.9 mg/l, respectively, which were about two-times higher than those obtained at pH 4 to 9.