Decarboxylative reaction of aliphatic carboxylic acids is a powerful tool for formation of aliphatic compounds in organic synthesis, because carboxylic acids occur widely in nature and are readily commercially available. Thus, a general method for the decarboxylative reaction of carboxylic acids under mild conditions is desired. In this paper, the author reports that alkyl radicals are generated in the decarboxylation of free aliphatic carboxylic acids by a radical cation of arene via photoinduced electron transfer. The generated alkyl radicals react with a variety of reagents such as thiols, alkenes, oxime ethers to yield the respective reduction and adduct products in high yields. This photochemical method represents a less toxic and milder process for formation of aliphatic compounds from aliphatic carboxylic acids via decarboxylation than conventional methods, because light is a clean and selective reagent.