We have developed a starch-based asphalt modifier, C-AG. C-AG disperses fibrously in asphalt, improving the flow resistance of asphalt and helping to prolong the life of roads. By means of using this newly developed asphalt modifier, energy consumption related to modified asphalt production and road construction is lower than that of conventional asphalt modifiers, and greenhouse gas (GHG) emissions are expected to be reduced.