The endophytic nitrogen-fixing bacterium Herbaspirillum rubrisubalbicans, strain AB7, was grown in synthetic liquid medium, containing mannitol and glutamate as carbon and nitrogen sources respectively, at 30^oC under agitation (120 rpm) until its late exponential phase (72 h). After cell removal by centrifugation the medium was concentrated and precipitated with 3 volumes of cold ethanol (-20^oC). The resulting precipitated was recovered by centrifugation, resolubilized and dialyzed against distilled water in a 6 kDa MWCO membrane for 48 h. The material retained inside the membrane was then freeze-dried to yield the EPS. A portion of the EPS was submitted to partial hydrolysis with 2M TFA at 100^oC for 30 min. After the acid had been removed, the material was solubilized in water and precipitated with cold acetone (3 v/v), to yield a low molecular weight-containing supernatant (EPS-ac) and a precipitate that was recovered by centrifugation. The latter was then resolubilized in water and precipitated with cold ethanol (3 v/v), which gave a soluble fraction (EPS-et) and a precipitate that was recovered by centrifugation and solubilized in water (EPS-ws). These three fractions were submitted to TLC analysis, revealing that the water soluble fraction (EPS-sw) was formed only by high molecular weight molecules, and both EPS-ac and EPS-et contained low molecular weight carbohydrates. The fractions were then submitted to analysis in GC-MS showing the presence mainly of Rhamnose, Allose, Galactose and Glucose, as their alditol acetate derivatives, with different molar ratios within each fraction. ¹³C-NMR analysis of EPS-ws showed four signals in the anomeric region arising at d 94.9, 100.0, 101.1 and 103.6. The deoxy C-6 signal of rhamnosyl units was found at d 16.8 and acetyl substituents were evidenced by the signals found at d 20.5 (-CH₃) and d 173.6 (C=O). DEPT experiment showed that hexoses were not glycosidicaly substituted at C-6 once all inverted signals were fount between 60.0 and 61.5 ppm. Partially methylated alditol acetates (PMAAs) derivatives of EPS-ws were analyzed by GC-MS and showed di- and tri-O-methyl hexose derivatives together with 3-O-Me- and 2-,3-O-Me₂-rhamnosyl units. HMQC, COSY and TOCSY analyses were also performed for EPS-ws and assignments of several correlation signals were determined.