Biodegradation of two alpha-methyl branched oxo-alcohol ethoxylates (OAE) of different polydispersity: LIAL 125/14 BRD (LIALB) (broad M.W. distribution) and LIAL 125/14 NRD (LIALN) (narrow M.W. distribution), both having an average of 14 oxyethylene subunits (EO) and a C(12-15) alkyl moiety were tested under the continuous flow activated sludge conditions of the classical Husmann plant. Primary biodegradation and concentration of metabolites: free oxo-alcohol fraction (FOA) and poly(ethylene glycols) (PEG), were measured. PEG were divided into two fractions: short-chained PEG (PEGshch) (1-4 EO) and long-chained PEG (PEGlch) (>4 EO). The indirect tensammetric technique combined with an adequate separation was used for analysis. Central fission was found to be a highly dominating pathway, as is the case with fatty alcohol ethoxylates. OAE are highly primarily biodegraded (above 95%). High concentrations of FOA and PEG are formed. Once formed the PEGlch are further fragmented into the PEGshch. Free alcohol fraction compounds are biodegraded sooner when alkyl moiety is shorter. OAE polydispersity has an influence on the kinetics of biodegradation; PEG formed from LIALN are biodegraded slower and to a lower degree than those from LIALB.