The lignite deposit at Pontokomi (Sector 6) in the Ptolemaida Basin of Greece was studied petrographically so that the conditions that prevailed in the paleo-environment could be analyzed. The above deposit is situated in the northwestern part of the broader basin of Ptolemaida in Macedonia, Greece. It consists of alternating beds of lignite and interbedded strata. The interburden is made of clay marls, occasionally enriched in sand. Thirty-seven samples of lignite were taken for analysis from two representative coreholes (Delta 3 and Delta 5) located in the central part of the lignite deposit. The study showed that macerals of the huminite group were dominant, followed by inertinite macerals. Liptinites made up a small percentage of the total population. Densinite, attrinite, eu-ulminite, corpohuminite and detrogelinite were the most abundant huminite group macerals, respectively. Inertodetrinite and fusinite were the dominant inertinite macerals, while sporinite and resinite were the predominant litpinite macerals. Mineral matter consisted mainly of clays, carbonates and pyrite. Detailed maceral analysis allowed us to obtain indices related to the wetness in the peat swamp (GI), degree of vegetation growth (VI), level of water table (GWI), and preservation of plant tissues (TPI). By comparing ratios of these indices and correlating them to ternary diagrams developed by different authors, we were able to obtain valuable information as to the conditions that dominated in the original peat swamp. The ratio of VI/GWI provided data on the hydrology and nutrient supply in the peat-forming environment, whereas the ratio of TPI/GI was used to interpret the paleo-environment in relation to the water table. Evaluation of the data showed that the environment that hosted the parent flora was limnic (open water) dominated by grasses and sedges under rheotrophic to mesotrophic nutrient supply conditions.