In this study, the efficiency of direct absorption solar collector (DASC) using carbon nanotube nanofluid in the mixture of water and ethylene glycol as the base fluid was experimentally investigated and compared with the efficiency of the flat plate solar collector (FPSC). The results show that the maximum efficiency of the DASC using the base fluid and absorptive bottom surface is about 4.7% and using carbon nanotube nanofluid is about 22% more than that of FPSC. According to the results, the performance of DASC with the application in the domestic solar water heaters, is better than FPSC at the same operating condition.