We have investigated the gas-phase UV photolysis of glycolaldehyde (HOCH2CHO) by laser photolysis combined with cavity ring-down spectroscopy. Absorption cross sections of glycolaldehyde in the 280-340 nm region were measured by cavity ring-down spectroscopy. The HCO + CH2OH and the OH + CH2CHO product channels following the photolysis of glycolaldehyde were directly examined. The average HCO quantum yields from the glycolaldehyde photolysis were 0.61 +/- 0.08, 0.59 +/- 0.05, 0.61 +/- 0.16, 0.66 +/- 0.09, 0.61 +/- 0.11, 0.65 +/-0.05, 0.47 +/- 0.04, 0.52 +/- 0.09, and 0.45 +/- 0.05 at 280, 285, 290, 295, 300, 305, 308, 310, and 315 nm, where the error quoted (1 sigma) represents experimental scatter. The average OH quantum yield from the photolysis of glycolaldehyde at 308 nm was 0.11 +/- 0.02, where the error quoted (1 sigma) represents measurement uncertainty. End products such as CO, H2CO, (CHO)(2), CH3OH, HCOOH, and CO2 were detected from the 308 nm photolysis of glycolaldehyde. The yields of CO, H,CO, (CHO)(2), CH3OH, and HCOOH were estimated. We also directly measured the rate constant for the reaction between the OH radical and glycolaldehyde. The rate constant obtained was (1.01 +/- 0.20) x 10(-11) cm(3) molecule(-1) s(-1), where the error quoted (1 sigma) represents measurement uncertainty. Atmospheric implications of the results are discussed.