Biogasification is the suitable biomass-to-biofuel technology in rural areas. In coastal communities, seaweed is an abundant feedstock for household biogas digester. However, biogasification requires expensive and dangerous chemicals for pH adjustment. Hence, Venerupis species shell was tested as pH buffer on biogasification of Undaria pinnatifida. Addition of 3% and 5% (w/w) shell at the start of digestion successfully started biogasification [86.4 ml CH4/g volatile solid (VS) and 109.5 ml CH4/g VS, respectively]. Biogasification efficiencies of shell setups (3% shell: 24.2%, 5% shell: 30.7%, and BH then 5% shell: 19.4%) were lower than in BH then NaOH (68.3%). Nonetheless, biogas start-up failed when shells are not added.