Oxalyl chloride, (ClCO)2, has been used as a photolytic Cl atoms precursor for kinetic and photochemical studies. Previous studies of the (ClCO)2 photodynamic at 193, 248, and 351 nm suggest that UV photodissociation proceeds via a two-step mechanism including formation of an excited ClCO* radical (1) and dissociation of a fraction of the ClCO* depending on the photolysis wavelength into Cl + CO (2): (ClCO)2 + hv → ClCO* + CO + Cl (1) ClCO*→ Cl + CO (2) The ClCO radical formed with the energy lower than its dissociation barrier has been found to undergo unimolecular dissociation (3) on the time scale of several microseconds at room temperature and atmospheric pressure: ClCO + M → Cl + CO + M (3) In this work the photodissociation of (COCl)2 by solar irradiation has been studied in the HELIOS environmental chamber. An effective (COCl)2 dissociation quantum yield of 0.34±0.03 has been derived from the measured actinic flux in the chamber and the observed (COCl)2 decay rate. This result is in agreement with previous studies. The relative yields of CO and Cl atoms were derived by comparing the (COCl)2 loss rate with the production rates of CO and Cl atoms. The Cl production rate was derived from the measured by CIMS steady state HO2 or CH3O2 radical concentrations generated by scavenging of Cl by H2 or CH4, respectively. The obtained relative CO yield of 2.2±0.1 is in agreement with previous studies. The relative yield of Cl has been found to be 2 times lower, 1.01±0.03, in disagreement with previous studies and suggesting another mechanism of the (COCl)2 photodissociation at wavelengths longer than 300 nm.