The woman from Shanghai, known only by her surname Fan, leaned too far forward from a ship deck and fell overboard, according to Chinese media.
She reportedly fell from the fourth deck, the approximate height of a seven-floor building.
The 31-year-old survived the ordeal with only minor injuries, reports said.
Ms Fan was on a five-day cruise on the Royal Caribbean from Shanghai to South Korea and Japan, according to reports.
She reportedly had nothing to cling on to after she fell in the sea, and drifted for most of the time until she saw a fishing boat approaching.
Her parents, who were allegedly on the cruise with her, did not realise she was missing until hours later.
Her father refused to believe his daughter was alive until he heard her voice on the phone, reports said.
The 1.75m tall woman had allegedly been enjoying the view on the cruise deck on Wednesday night when she accidentally fell forward into the sea.
She called for help but was not heard.
She eventually became exhausted, yet somehow managed to tread water while dozing off, Chinese media said.
She spotted a fishing vessel when she awoke on Friday morning.
Fan is said to have escaped with only blisters on her arms caused by jellyfish stings.
Some users took to micro-blogging site Sina Weibo to express their incredulity.
“She didn’t eat and drink at sea for 38 hours and she survived? That’s a miracle,” said one user.
Source: BBC