Desugarized sugar beet molasses is a high-salinity side stream after fractionation of beet molasses by chromatography. It could be demonstrated that this by-product of the sugar industry is a suitable substrate for the production of poly(3-hydroxybutyrate) with the halophilic bacterium Bacillus megaterium uyuni S29. Cell dry mass concentrations of up to 16.7 g L-1 with a P(3HB) content of 0.6 g g(-1) were achieved after only 24 h of batch cultivation. Utilization of a desugarized sugar beet molasses medium resulted in a two- to threefold increase in biomass production compared to a conventional mineral based medium. Depending on the extraction method, the molecular mass (M-n) of the P(3HB) varied between 119 kDa and 722 kDa. The high P(3HB) productivity of 0.42 g L-1 h(-1) during batch experiments combined with desugarized sugar beet molasses as inexpensive substrate suggests a simple and robust process for cost effective P(3HB) production.