This paper investigates the presence and concentration levels, of n-alkanes and also the potential sources of contamination of surface sediments in the fishing village Z-3 in the city of Pelotas, Brazil. The extraction of the sediments was performed according to EPA method 3540 and the separation of aliphatic hydrocarbons was done with preparative column chromatography. Gas chromatographic analysis with flame ionization detector was employed for the identification and quantification of compounds The level of aliphatic hydrocarbons found, was due mainly to n-alkanes originated from weathering of terrestrial plants and algae production. It is also possible to observe the dilution effect of the lagoon about analyzed compounds, comparing the results obtained from different sampling points. In general, the sediments sampled in the investigated region presented small levels of contamination by hydrocarbons