Skin-attachable wearable devices including triboelectric nanogerators (TENGs) and self-powered sensors will have biofriendly and biocompatible issues, because they can directly interact with the human body. Based on the diatom frustule and chitosan, known as biocompatible ocean biomaterials, we developed a chitosan-diatom TENG for biofriendly and skin-attachable wearable devices. The highly porous diatom frustule, which is naturally abundant and mass-producible from mega-scale ocean environments, can be used as a biocompatible additive to greatly change electro-positivity and surface properties of chitosan films, showing bio-affinity and much higher output power. The time averaged power density of the chitosan-diatom triboelectric nanogenerator is measured as 15.7 mW/m(2), which is 3.7 times higher than that of the pure chitosan TENG. For practical applications, the electrode-encapsulated chitosan-diatom film is successfully applied for a self-powered watch and a skin-attachable motion sensor. We believe that the diatom bio-silica can be used to make a synergy with other biomaterials for achieving the high power of TENGs for the skin-attachable wearable devices.