Black carbon (BC) is a term used to represent the continuum of charred materials produced during incomplete combustion of fossil fuel and biomass. Since the emission rates of BC are increasing in the last decades due to energy requirements from modern human population, there is great interest in the distribution of BC in the environment (atmosphere, water and sediment) because their role in the biogeochemical cycle of carbon is not fully understood and, also, because the high adsorption capacity of BC particles may decrease the bioavailability of organic contaminants (PAH, for example). In the present work it was determined the distribution, for the first time ever, of BC in superficial sediments from Guanabara Bay and it was evaluated the relation between BC (quantified in the present work) and known concentration of polycyclic aromatic hydrocarbons (PAHs) in sediment cores from 3 mangrove regions in the bay (Suruí, Nova Orleans and Piedade). Two analytical protocols for BC quantification were compared (chemical oxidation with dichromate/sulphuric acid and thermal oxidation at 375 ºC), and the second one was chosen for routine analysis. After treatment, the BC content was measured by a dry-oxidation method in a Carlo Erba EA110 elemental analyser. Total organic carbon (TOC) was also measured using the same instrument. In the superficial sediments (0-2 cm) from Guanabara Bay, the mean BC carbon content (n = 25) was 0.19 +- 0.07 % (dry-weight mass), ranging from 0.03 % to 0.31 %. The percentage of BC to TOC was 5,35 +- 2,45 (n = 25). The sediments in the northern sector of the bay had higher contents of BC, what is related to the input of pyrolitc materials from river and urban runoff and local restricted water circulation. In the mangrove sediments, the BC content was 0.11 +- 0.08 % (dry- weight mass) and the BC:TOC fraction was 1.99 +- 1.59 % (n = 62). Linear regression and principal components analysis revealed that the distribution of PAH is closed related to the BC contents in the sediment from Suruí and Nova Orleans, but not for Piedade sediments, probably due to uncertainties in the origin of PAHs in these sediments. An experiment with fortification of sediment with pyrene confirmed the importance of adsorption of PAH to the BC particles. In conclusion, the data obtained in the present work permitted a better understanding of the different fractions of organic matter in the sediments from Guanabara Bay and showed the importance of BC in the fate and possible effects of PAH in this coastal contaminated system.