Amazon.com says it is buying Quidsi, the owner of Diapers.com and Soap.com, for $500 million in cash in a move to expand its online retail empire.

Amazon.com Inc. said Monday that Quidsi will continue to operate independently after the acquisition.

Amazon says it will also assume about $45 million in debt and other obligations as part of the deal. The acquisition is expected to close in December.

Amazon, based in Seattle, bought popular online shoe retailer Zappos.com, for $850 million last year.