Littorina flava is used as bioindicator to measure environmental impacts and to assess the quality of the environment and how it changes over time. The main objective of this work was to determine the reproductive characteristics of L. flava and its relationship with environmental variables and the influence of contaminants in a rocky coast of Mel Island, Paraná, Brazil. Monthly sampling during eight months were performed in the intertidal region during spring low tide in two periods (Winter/Spring and Summer/Fall) in three levels (Upper, Middle and Lower) with three replicates (A,B,C). Monthly 40 individuals of L. flava were collected in the three levels. Environmental parameters: air and water temperature and water salinity were also obtained. The organisms collected were measured (height - H and width - W), examined for sex identification and gonadal maturation stage. Gonad maturation of L. flava was verified in the end of the first sampling cycle (Winter/Spring). Sexual intercourse behavior was observed. In September and October 2010. This reproductive behavior was less observed in the second period (Summer/Fall) together with a decrease in the gonads maturation. Sexual proportion demonstrated high predominance of males, indicating a possible imposex occurrence due to pollutants verified in the area (fuel from boats, sewer discharge).