This work evaluated the results of water absorption tests on samples of expanded polystyrene (EPS) in the specific masses of 10, 20 and 30 kg / m³, molded in specimens with cubic dimensions of 100 mm. The tests were carried out based on ASTM C272 (2001). Initially, the natural mass (at room temperature) of the laboratory-conditioned samples was measured as prescribed by the standard, to subsequently obtain the hygroscopic moisture of the material. Then the specimens were placed in a greenhouse at a temperature of 95° C for a period of 24 hours in order to obtain their dry mass. The next step was to obtain the saturated mass by immersing the samples in distilled water for 24 hours after that period, these samples were taken from the vessel and dried to remove surplus water on the surface and then weighed on a high precision scale. Long-term water absorption tests were also performed, which differs from the simple test by the immersion time of the samples, in which the test bodies were kept submerged for a period of 28 days, seeking to study the behavior of the EPS when exposed or in contact with water for long periods of time. From the results it was observed that the water absorption parameters tend to decrease with the increase of the specific mass, being that the lower density presents significant water absorption, this shows that there is a loss of the beneficial characteristics of the use of EPS with low density. Thus, it is important to provide a waterproofing system in practice that avoids the direct contact of the geoexpandido with the water, as well as an adequate and efficient drainage system to remove the water in contact with the EPS faster in the construction. It is also worth noting that water absorption represents about 4% of the sample volume and the behavior, both in mass and volume, for immersion in a 24-hour period and 28 days remains similar.