This is a preliminary study of the wave action over the continental shelf of the State of S. Paulo, Chart I figures a theorical 180 m. long wave as would be produced by an eastern polar anticyclone. The waves will strike the coast at right angles with a slight divergence along the whole coast of the State; reaching a maximum at Santos and a minimum at Cananeia. Chart II, figures the waves, incidence at Cananeia; it can be pointed out that the island of Bom Abrigo offers no protection against a wave coming from the east and that this wave penetrates easily along the pass leading to the inland waters of the region of Cananeia.