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The use of ultrasonic technique for detection of internal flaw and delamination in concrete structures is extremely difficult. In this research all traditional techniques were precisely studied and four new inspection techniques were developed which could be practically applied in testing concrete structures. The developed techniques are: (1) Detached Receiver Through Transmission technique(DRTT); (2) Direct testing of rebars in concrete structures; (3) Semi-Through Transmission Technique(STT); (4) Detached Receiver Pitch-Catch Technique(DRPC). All four of the developed techniques have low signal responses and resolution is critical. The detached receiver techniques have low responses because most of the signal is reflected at the concrete surface rather than transmitted into air. The relatively long concrete path and rebar path with the semi-through transmission method attenuate the response signal. The key to improving the methods developed is to improve the signal responses obtained. The techniques developed, however, present potential solutions to the problem of evaluating the subsurface degradation in concrete structures. The lab testing of these techniques on concrete specimens presented successful results in locating known unbonded regions when the thickness of the specimen was less than 20 cm. The field testing was performed on the concrete structures more than 20 cm in thickness which resulted in weak signals, but explained most of the known surface and subsurface discontinuities in the concrete beam.