The collector efficiency of double-flow solar air heaters with fins attached by baffles, has been investigated experimentally and theoretically. The double-flow device was constructed by inserting the absorbing plate into the air conduit to divide it into two channels, upper and lower channels. Theoretical predictions are qualitative agreement with the experimental results. Both the theoretical predictions and experimental results showed that the optimal fraction of airflow rate in the flow channels is around the value of 0.5. The effect of baffle density on the collector efficiency has been also presented and discussed.