As expanding the usage of adhesives in automotive bodies, non-destructive inspection techniques for them are increasingly required. The aim of this study is to evaluate adhesive regions with non-contact air-coupled ultrasonic technique. First, ultrasonic transmittance of steel plates was investigated theoretically and experimentally. As a result, transmitted waves at adhesive regions can be detected using oblique incidence and reception where the sensor angle is adjusted to the critical angle of A0 mode of Lamb waves. Secondly, images of the adhesive regions were obtained by scanning ultrasonic sensors and taking amplitude distributions of transmitted waves.