Abstract: Contamination due to petroleum hydrocarbons may result from many sources. In Mauritius, coastal sediment pollution results mostly from anthropogenic sources such as industrial activities and the sea activities, mainly at the harbour. While some authors affirmed that sea activities polluted the coastal sediments, and the concentration of pollutants was found to be higher in the harbour, likewise, an investigation was set to quantify the amount of total petroleum hydrocarbon (TPH), ranging from C10 to C40, in the neighbouring coasts from the Mauritius harbour at Port-Louis and to determine its effect on the coastal ecosystems. Three coastal sites were selected, namely, Tombeau Bay (C-BDT), Pointe aux Sables (C-PAS) and Mer Rouge (C-MER). Results showed that the most polluted the coastal sediments was Pointe aux Sables (451 mg/kg) followed by Tombeau Bay and Mer Rouge (less than 66 mg/kg) both. Despite that the chemical properties of the sediments analysed were favourable for microbial biodiversity, results showed that there was a much richer microbial biodiversity in less contaminated sediments while greater microbial activity (respiration rate) in the contaminated environment, C-PAS. Given that the toxicity of TPH in soil was established at range greater than 1000 mg/kg, it was noted that despite the C-PAS site was the most polluted, it did not reach the permissible limit. However, due to the urbanisation and intensive use of the sea for ship activities, the concentration of the level of pollution due to TPH is expected to increase in the forthcoming years.