Mangroves are an ecosystem that features dark colored sediment, rich in organic matter, with humic substances as its main component, which were the target of this work that aimed to characterize those humic substances chemically and spectroscopically and compare the biological activity of different humic materials isolated from mangrove areas with different levels of anthropic interference (Maria Ortiz high and Canal dos Escravos low). The chemical and spectroscopic characterization of the humic materials was performed through the analysis of elemental composition, E4/E6 ratio, fluorescence intensity and infrared and their biological activity was tested by evaluating changes in the root growth of corn seedlings in hydroponics. The humic materials, from the Maria Ortiz area, presented higher values in the C/N ratio, higher values in the fluorescence index and lower values in the E4/E6 ratio, when compared with the humic materials from the area of Canal dos Escravos. The absorption bands of the infrared spectrum indicated similarities with respect to the chemical functionality of the humic materials, however, it was possible to notice clear differences between the study areas. All humic materials promoted, in general, changes in the root architecture of corn seedlings when compared to the control treatment. This work shows that there are differences in the chemical and spectroscopic characteristics and in the biological activity of the studied humic materials, demonstrating that the anthropic activity alters the quality of the organic matter of the mangrove sediments, which may interfere in the survival and development of the mangrove forests.