The concentration and distribution of aromatic biomarkers in Coals and Shales from five boreholes penetrating the Maastrichtian Mamu Formation of the Anambra Basin, southeastern Nigeria, was investigated by gas chromatography-mass spectrometry in order to assess the thermal maturity and organic matter input. The study focused on the variations of the relative abundances of naphthalenes, phenanthrenes, monaromatic and triaromatic steroids identified on the mass fragmentograms. Trimethylnaphthalene (TMN) is the most abundant of the naphthalene family while methylphenanthrene (MP) is the most abundant of the phenanthrene family. The relative abundance of the sum total of the phenanthrenes and their isomers was greater than that of the naphthalenes. The distribution of these aromatic hydrocarbons and their akyl derivatives was strongly controlled by selective expulsion mechanism and thermal maturation of organic matter. The low dibenzothiophene/phenanthrene (DBT/PHEN) ratios (0.01-0.06) as well as the enhanced concentrations of 1, 2, 5- TMN relative to 1, 2, 7- TMN points at organic matter derived mainly from higher plants while extract ternary plot of C27, C28 and C29 monoaromatic steroids suggest a Type III and mixed Type II/III kerogen. The calculated mean vitrinite reflectance (%Rm) determined from the distributions of the isomers of methyldibenzothiophene ratio (MDR) in the rock extracts range from 0.51 to 1.43. These maturity values show that the Coal and Shale extracts are marginally mature for hydrocarbon generation.