The aim of the study is to examine by geochemical proxies the effect of biodesulphurisation on coal organic matter composition. Two Bulgarian and one Turkish low rank coals (R-r = 0.20-0.46%) were analysed. Prior to biotreatments, the coals were demineralised and depyritised. The white rot fungi Phanerochaete chrysosporium - ME446 and the thermophilic and acidophilic archae Sulfolobus solfataricus - ATCC 35091 were used. After desulphurisations the samples were extracted with chloroform to recover bitumens. Maltenes (portion soluble in n-hexane) were prepared after asphaltenes precipitation. They were fractionated into aliphatic, aromatic and polar fractions and the first two were GC/MS studied. The following homologous series were registered: (i) n-alkanes, nC(12)-nC(32), mainly long-chain homologues with "odd'' members prevalence; (ii) n-alkan-2-ones; (iii) esters of n-fatty acids, nC(12)-nC(32), with bimodal distributions; (iv) diterpenoids; (v) products of triterpenoids destruction and aromatisation; (vi) hopanoids. Results were quantitatively interpreted. All studied fractions of initial and biotreated samples were strongly dominated by n-alkanes, 60-90%, but patterns of distributions after desulphurisations were somewhat changed as shorter homologues had partly disappeared. Relative distribution of geochemically considered series depicted some peculiarities: (i) organic matter of higher mature coal was less attained by desulphurisation; (ii) lignite organic matter seemed to be more susceptible to biotreatment especially with P. chrysosporium culture. During S. solfataricus biodesulphrisation different series preserved their pattern of distribution while P. chrysosporium treatment strongly perturbed it. There were indications for coal organic matter oxidation assigned by polar biomarkers appearance. Tercyclohexanes were detected only in products of coals biotreated with S. solfataricus. The gradual changes in organic matter composition depicted by a scale adopted from petroleum exploration attested "light'' biodegradation during coal biodesulphurisation. (C) 2014 Elsevier Ltd. All rights reserved.