A reaction system has been studied for the production of C-12 and C-18 hydrocarbons from sorbitol by reduction with a hydroiodic acid (HI)-phosphorous acid mixture. The effects of reaction conditions on the yield and selectivity of hydrocarbons have been investigated. It was found that both the increase in the water content and decrease in the HI amount lead to the decrease of the yield and increase of selectivity for hydrocarbons and water exhibits greater effect than HI. The yield of hydrocarbons was found to increase with time but did not change too much after the reaction proceeded for 14 h. A maximum yield of 62.07% for hydrocarbons was achieved at a water content of 34%, a sorbitol/hydroiodic acid/phosphorous acid molar ratio of 1:3:8, and a reaction time of 12 h. The possible reaction mechanism, we think, is the umpolung of the C-I bond and eventually the formation of the C-H bond plus the polymerization of unstable halocarbons, which results in the formation C-12 and C-18 hydrocarbons.