The service has been down since Monday night, but bank spokesman Thomas Kelly couldn't specify the exact time service was disrupted. Chase has 16.5 million customers who bank online.
ATMs at Chase, the nation's second-largest bank, were not affected. The bank's telephone banking service was also operating normally.
A note on the website for Chase, www.chase.com, says: "Our website is temporarily unavailable. We're working quickly to restore access. Please log on later."
Chase bank is part of JPMorgan Chase & Co.