School spokesman Jonathan Gust says the incident occurred about 2:30 p.m. Tuesday in a lab on the third floor of Mendel Hall. The building was evacuated.
Gust could not offer details of what happened or what materials were involved in the experiment.
Police, fire and other emergency officials responded, and one student who had experienced breathing problems and nosebleeds was taken to a hospital.
Radnor police said about nine others were treated on scene and at least some were to be taken to hospitals to be checked out as a precaution.
Villanova is a private Catholic university in suburban Philadelphia.