This study investigated in vitro effects of bacterial lipopolysaccharide (LPS) on ram sperm motion parameters at concentrations less than its spermicidal effects. After incubation of epididymal sperm samples for 45, 90, 135, 180, and 225 min in the presence of LPS (50, 100, 200, and 400 µg/ml), motion parameters were evaluated by computer-aided sperm analysis. There was no significant increase of the fast progressive motility (class A) of sperm in LPS-treated groups at different times while there was a decrease in the slow progressive motility (class B) and the non-progressive motility (class C) of sperm in LPS-treated groups at different times that were only significant (P < 0.05) at the 135 min (classes B and C) and 180 min (only class C) incubation times and at concentrations of 200 and 400 µg/ml LPS compared to their controls. Concentrations of 100, 200, and 400 µg/ml LPS caused an increase in linearity; the wobble, mean angular displacement, and the amplitude of lateral head displacement decreased significantly (P < 0.05) at different times (45, 90, 135, 180, and 225 min). It can be concluded that LPS, at concentrations less than its spermicidal effect, changes progressive motility and motion parameters that probably lead to infertility.