Stable liquid pharmaceutical compositions comprising an antagonist anti-CD40 antibody as a therapeutically or prophylactically active component and methods useful in their preparation are provided. These compositions comprise the antagonist anti-CD40 antibody, a buffering agent to maintain the pH of the composition between about pH 5.0 and about pH 7.0, and an amount of arginine-HCl sufficient to render the liquid composition near isotonic. The stable liquid antagonist anti-CD40 antibody-containing pharmaceutical compositions of the invention find use in methods for treating proliferative diseases and diseases having an autoimmune and/or inflammatory component.