A method is proposed for measuring CO2 emission by tree rings. The method is aimed at finding new characteristics of tree rings. Rings of a Scots pine (Pinus sylvestris L.) and Siberian spruce (Picea obovata Ldb.) were taken as an object of investigation. The CO2 concentration was measured with a laser photoacoustic gas analyzer. Positive correlation was found between the emission of CO2 and the ring width.