Organic fractions assessment in influent wastewater is essential for designing the biological wastewater treatment plant. The characteristics of the influent organic load (readily biodegradable, biodegradable, or inert) and form of distribution (soluble/suspended) may induce the design and operational parameters of primary settlers and biological treatment step. The current work presents the comparative assessment of organic fractions in three wastewater samples evaluated experimentally through three different fractionation methodologies, respectively modified ATV-A131 guidelines, IWA methodology, and the Łomotowski-Szpindor methodology. The wastewater samples were collected from the influent of two municipal wastewater treatment plants. In all wastewater samples tested the biodegradable fractions SS or XS had the highest share in the total COD. This is consistent with the biodegradable character of municipal influents and the suitability for organic and advanced nutrient removal through biological processes. The amount of non-biodegradable fractions SI and XI, varied from 18 to 54% of total organic load, on momentary grab samples of studied influents.