Photos of the newlyweds at the Vatican museums, including the Sistine Chapel, hit Twitter Monday, Italy's ANSA news agency reported.
The owner of the exclusive Pierluigi's restaurant in Rome told local news sources the couple was on their honeymoon and ate an "intimate and romantic fish dinner" on Sunday evening.
Zuckerberg and Chan were married in Palo Alto, Calif., May 19, the day after Facebook made its stock market debut.
The wedding was a surprise for the 100 guests who were told they were gathering to celebrate Chan's recent graduation from University of California, San Francisco.
Susan Sarandon 'very excited' about daughter's pregnancy
Jessica Simpson shares three-way kiss with friends in photo