Recently, there have been many studies on the adhesion mechanisms of various mollusca such as snails, clams and octopi. Understanding their magnitude and working force is advantageous for application in specially designed robotic systems. The adhesion mechanism in these animals is effectively generated by a complex biological system that is able to operate under various surface conditions. In this work, fundamental research was conducted to understand the adhesion mechanism of living snails. Pull-off and lateral forces were measured while the snail was adhered to various surfaces in order to investigate the effects of surface conditions such as surface energy, surface roughness and surface type on the adhesion or suction of the snail. In order to understand the relationship between suction and adhesion of the snail, pull-off and suction forces were simultaneously measured using a custom-built apparatus. The average adhesion and suction force was estimated to be 0.2 kgf and 0.44 kgf, respectively. It was found that the snail effectively used both capillary adhesion and suction mechanisms to attach to and move on the surface.