Small oligonucleotides (di- and trimers) were investigated by atmospheric pressure photoionization (APPI) with focus on the fragmentation mechanisms. The fragmentation patterns of these biomolecular ions have been monitored under dopant-assisted photoionization (DA-APPI) conditions. Our results reveal new aspects of the gas- phase chemistry of ions formed from such biomolecules. They illustrate that the reaction between low-energy electrons released from photoionization processes and di- and trinucleotides lies in dissociative electron attachment processes leading to phosphodiester bond cleavages and to the formation of numerous fragments in the ion source. The conditions of DA-APPI, which involve protic solvents and atmospheric pressure conditions, seem to be relevant for the study of radiation damages to biological molecules.