A critical issue in using adhesives for structural joints is the assessment of integrity and reliability of these joints in service. One of the factors limiting the wide spread use of adhesives for structural bonding in industries is the lack of reliable non destructive testing methods to evaluate the bonded joints. Joining of fiber reinforced polymer (GFRP) composite materials by adhesive bonding has to take into account factors such as the adopted bonding process, the interface properties and the control of the adhesive bond line thickness. In this paper, results of experimental investigations on the non destructive evaluation (NDE) of single lap bonded joints made of glass fiber reinforced epoxy matrix composite laminates are presented. Unidirectional glass fiber reinforced plastic substrates were joined using a two part epoxy adhesive system. Specimens with varied bond quality were prepared adding different proportions of poly vinyl alcohol (PVA) to the epoxy hardener mixture. The bonded area of the specimen was subjected to ultrasonic inspection and x-ray radiography. The joints were subsequently loaded till failure to determine their bond strength. Results obtained show a correlation between the amplitude of reflected ultrasonic waves from different interfaces and the bond strength.