All-glass evacuated tube solar collectors consist of glass evacuated tubes and absorber tubes. Solar thermal energy from the sun is transferred to the working fluid through the glass evacuated tube and the absorber tube. Several collectors which have different absorber tubes are tested to find the effects of the absorber tube shapes and the operating conditions such as the incident heat flux and the flow rate. As the results, the efficiency of the collector which has a finned tube U tube is about $2{sim}5%$ higher than that of the others in all cases on an average. And the collector has a finned U tube has the highest efficiency at the high flow rate and the low incident heat flux. In this condition, the outlet mean temperature is low and the heat loss becomes small. Also, it is known that the fin effect is greater than the shade effect.