Lipopolysaccharide (LPS) may participate in ruminal acidosis by affecting ruminal bacteria.This study determined how LPS affects the growth of pure cultures of rumen bacteria, including those that contribute to acidosis. Concentration of LPS in this study was 200,000 EU. Optical density (OD, 600 nm) measurements were collected until bacterial growth reached plateau. Once bacterial growth reached plateau, culture media was collected to measure pH and determine fermentation end products. Logistic function was used to predict the growth rate and lag time based on OD₆₀₀. Cellulolytic bacteria (Ruminococcus albus 7, Ruminococcus flavefaciens FD-1, Fibrobacter succinogenes S85), starch-utilizing bacteria (Streptococcus bovis JB1, Succinivibrio dextrinosolvens 24, Lactobacillus ruminis RF1, Selenomonas ruminantium HD4), and lactate-utilizing bacteria (Megasphaera elsdenii T81) were first tested. Growth rate and lag time of cellulolytic and lactate-utilizing bacteria were not affected by LPS dosing (P > 0.05). However, LPS dosing increased growth rate of starch-utilizing bacteria by at least 5% (P < 0.05). Except for L. ruminis RF1, lag time of other tested starch-utilizing bacteria was decreased by LPS dosing (P < 0.05). Then a defined media with LPS as the only carbon source was used to culture S. bovis JB1 and it was observed that S. bovis JB1 could not grow on it. Then glucose was sequentially added to these defined media and the growth rate of S. bovis JB1 was increased by 15% (P < 0.01) and lag time was decreased by 12% (P < 0.01) on LPS media compared with the control. Finally, detoxified LPS (200,000 EU, lipid A delipidated) was dosed to test toxicity of LPS to S. bovis JB1 and M. elsdenii T81. M. elsdenii T81 was not affected by detoxified LPS. Growth rate of S. bovis JB1 was increased by 8% in detoxified LPS (P = 0.02) and 16% in normal LPS (P < 0.01); lag time was decreased by 3% in detoxified LPS (P = 0.28) and 14% in normal LPS (P < 0.01). In sum, LPS stimulated growth of rumen bacteria that use starch and produce lactate. Our results suggest that LPS is not only produced during acidosis, but it may also contribute to acidosis’ development.