Thirty two compounds of fatty acids were found in a 50 cm sediment core taken from Conwy Estuary, United Kingdom. Their distribution pattern changed with depth from short chain fatty acids (C12 - C20) predominance to long chain compounds (C21 – C25). The decrease of short chain fatty acids along the core suggested that early diagenesis occurred due to microbial and chemical degradation. The increase of longer chain compounds was probably caused by greater preservation or greater contribution from terrestrial organic matter. The percentage of branched fatty acids, odd/even and 18:1ω7/18:0 ratios showed similar distribution, linking them with bacterial activity in the sediment. Principal Component Analysis (PCA) separated the terrestrial derived fatty acids (long chain compounds) from the marine (short chain saturated compounds, mono and polyunsaturated fatty acids) and bacterial (odd chain length with their branched derivatives and 18:1ω7 acid) derived compounds.