Measurement of $C_2$, CH and OH radicals in the propane-air laminar flame was conducted using the digital imaging technique. And this technique has been applied to two kinds of flames which are fuel lean and fuel rich mixtures respectively. The limits of its application and the measurement accuracy has also been described for this measuring system. Despite the technical limitations of each parts consisting the imaging system, we could discern the reaction zone and understand the characteristics of the radicals there. Spatial distribution of each radical in the reaction zone gave information enough to understand the reaction mechanisms of $C_mH_n$ flame. $C_2$ radical image appeared first in the unburned side of the reaction zone, and then CH, OH radicals downstream.
