Officers responded to Bridges Academy at 1702 McLaughlin Avenue around 8:20 a.m. after a school custodian reported finding a backpack containing the bottle to the principal, who then called police.
It appears, the label on the bottle was handwritten.
The school was evacuated and traffic on McLaughlin between Bacchus and Audubon drives was blocked.
Officers will test the liquid before they dispose of it, San Jose police Sgt. Enrique Garcia said at 10:35 a.m.
Stay with ABC7 News for the latest details on this developing story.
ABC7 News contributed to this story.