Arsenobetaine is an organoarsenic compound that is the main source of arsenic found in fish. It is the arsenic analog of trimethylglycine, commonly known as betaine. The biochemistry and its biosynthesis are similar to those of choline and betaine.

Arsenobetaine is a common substance in marine biological systems and unlike many other organoarsenic compounds, such as dimethylarsine and trimethylarsine, it is relatively non-toxic.