We have studied the gas-phase photolysis of 4-oxo-2-pentenal by laser photolysis combined with cavity ringdown spectroscopy. Absorption cross sections of cis- and trans-4-oxo-2-pentenal have been measured in the 190-460 nm region. The product channel following 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal was investigated. The HCO radical is a photodissociation product of 4-oxo-2-pentenal only at 193 and 248 nm. The HCO quantum yields from the photolysis of a mainly trans-4-oxo-2-pentenal sample are 0.13 +/- 0.02 and 0.014 +/- 0.003 at 193 and 248 nm, where errors quoted (1 sigma) represent experimental scatter. The HCO quantum yields from the photolysis of a mainly cis-4-oxo-2-pentenal sample are 0.078 +/- 0.012 and 0.018 +/- 0.007 at 193 and 248 nm, where errors quoted (1 sigma) represent experimental scatter. The endproducts from 193, 248, 308, and 351 nm photolysis of 4-oxo-2-pentenal (the 4-oxo-2-pentenal sample had a tran/cis ratio of 1.062:1) have been determined by FTIR. Ethane, methyl vinyl ketone, and 5-methyl-3Hfuran-2-one have been observed, suggesting the occurrence of 4-oxo-2-pentenal photolysis pathways such as CH3COCH=CHCHO + h nu -> CH3 + COCH=CHCHO, CH3COCH=CHCHO + h nu -> CH3COCH=CH2 + CO, and CH3COCH=CHCHO + h nu -> 5-methyl-3H-furan-2-one. The estimated yields for the CH3 + COCH = CHCHO channel are about 25%, 33%, 31 %, and 23% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH3 + COCH=CHCHO yields are within 55% at 193 nm, and 65% at 248, 308, and 351 nm. The estimated yields for the CH3COCH=CH2 + CO channel are about 25%, 23%, 40%, and 33% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of CH3COCH=CH2 yields are within 80% at 193 and 248 nm and 65% at 308 and 351 nm. The estimated yields for the 5-methyl-3H-furan-2-one channel are about 1.2%, 2.1%, 5.3%, and 5.5% at 193, 248, 308, and 351 nm, respectively. The absolute uncertainties in the determination of 5-methyl-3H-furan-2-one yields are about 23%, 86%, 40%, and 46% at 193, 248, 308, and 351 nm. Results from our investigation indicate that photolysis is a dominant removal pathway for 4-oxo-2-pentenal degradation in the atmosphere.