An efficient one-pot direct dihydroxylation of alkenes has been achieved. This reaction proceeds under transition-metal-free conditions and in water solution, producing the corresponding 1,2-diols in good to excellent yields. The discovery of an optimal pH environment is identified as a key factor in the current system, which ensures the generality and good functional group compatibility of this reaction. Moreover, the gram-scale dihydroxylation of alkenes was demonstrated and without significant decrease of the yield of product, making this protocol very practical.