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The aim of this work is the study of the anaerobic treatment of wastewater with high molasses content and the determination of the optimum conditions for the efficient operation of an anaerobic digestion system, for the maximum pollutants removal and biogas production. The study of the anaerobic digestion carried out using a wastewater sample from the effluents of a baker's yeast industrial plant. Two Upflow Anaerobic Sludge Blanket reactors (UASB) were used, a laboratory system and a pilot scale unit. Samples from influents and effluents from both units were collected and were analyzed for the determination of quality parameters, such as organic matter content COD (total and soluble), total solids (TS), volatile solids (VS), and total suspended solids (TSS), nitrogen compounds (nitrates NO3, ammonium NH4 and total nitrogen TN), phosphates and pH. Inoculation of the anaerobic reactors took place by the addition of a sample received from the content of the full scale plant used for the treatment of the effluents from the baker's yeast manufacturing faciltiy. From the long term operation of the units it was revealed that effluents contained low COD, as a result of the efficient operation of the system and the organic matter removal. COD removal rates ranged from 35 to 40%, while the lowest removal values were observed at longer organic loading values. In addition, the biogas production rate was quite high, reaching up to 1500 L/day, during the period of stable operation. However, under conditions of high organic matter loading, a reduction of biogas production rate was observed, to about 1200 L/day. Generally, the increase in the organic loading rate and the reduction of HRT had a negative impact on the performance of the reactor.