Our environment has been affected by increasing concentration of organic and inorganic pollutants from anthropogenic sources. Perfluorinated compounds are an important source of pollution, and they are major risks for the aquatic ecosystems. Perfluorooctane sulfonate (PFOS) and Perfluorooctane sulfonyl fluoride (POSF) are both industrially synthesized per-fluorinated chemicals, and they produced in substantial amounts. They are found widely in surface water and aquatic sediments. In this study, the comparative embryotoxicity of increasing concentrations of PFOS (five concentrations ranging from 0.5 to 10 mg/L) and POSF (five concentrations ranging from 0.5 to 10 mg/L) were examined on embryos of the sea urchin, Paracentrotus lividus. Results were evaluated by observing: larval malformations, developmental arrest and embryonic/larval mortality. The results indicated that, low concentrations of these chemicals generally caused malformations in the skeletal system. It was observed that high concentrations (10 mg-PFOS/L, 10mg-POSF/L) inhibited the growth of embryos in the early life stages. As a result, POSF was more toxic than PFOS (EC50: 1.795 mg/L) on sea urchin embryo as the EC50 is 1.074 mg/L and also both of the chemicals were harmful on the embryonic development of sea urchin in the sense of whole embryo and cellular level. In conclusion, PFOS and POSF present a major risk to the normal development of P. lividus in the environment, so that it has ecological importance due to the hazard at a population level considering the cumulative effects of other environmental pollutants.