This paper presents the applicability of super-lightweight concrete to port structures particularly to gravity type concrete structures as caissons. Therefore, the presented study is a counterintuitive approach because gravity structures need to be heavy enough to resist external forces by their own weight. Weight reduction of caissons, which have grown in size nowadays, is a promising area of technology because a substantial structural weight reduces cost, diminishes execution restriction, and so on. Super-lightweight concrete with exceptionally low specific gravity of 1.2 to 1.8 has recently been developed, which is made of artificial lightweight aggregate of below 3% of absorption ratio with individual pores. This makes high durability and excellent mechanical properties compared to those of conventional lightweight concrete. The applicability of this super-lightweight concrete to caissons was evaluated from the viewpoints of execution and mechanical performance. Fundamental mechanical properties such as ultimate flexural and shear strengths and bond-slip behaviors were examined. The period and cost of manufacturing a caisson can be considerably reduced by using the super-lightweight concrete.