Molecular evolution is calculated in migrating fluid parcels in a protoplanetary disk considering gas-phase and grain-surface reactions. Radial distribution of molecules is obtained, which depends on ionization rate, temperature and/or desorption rate in the disk. If the temperature is high enough (> 20 K) or non-thermal desorption is efficient enough to sublimate dominant species such as CO in the comet forming regions, the desorbed species are transformed to less volatile species and again incorporated into ice mantles. Chemistry in these outer disks is similar to that in molecular clouds; it produces both oxidized and reduced species with a high D/H ratio.