It's the first time a Korean novel has made it on the list, according to Shin's agent Lee Ku-Yong, president of KL Management.
Shin, 48, is one of South Korea's most acclaimed novelists but "Please Look After Mom" is her first book to appear in English. Now she hopes she's set a globalising trend for other Korean writers.
"I am getting all these congratulatory messages but it (the success) doesn't feel so real yet," she told AFP in a phone interview from the United States.
"But, if I think about it, it's marvellous and I feel like I have achieved something new in a different world."
The book tells the story of an elderly, disorientated and illiterate mother from the countryside who gets separated from her husband at Seoul's busy train station and goes missing.
Her grown-up children distribute fliers and search the city for her, racked with guilt that none of them went to the station to meet their parents.
The story is told from the different perspectives of the husband, the children and the mother herself.
Shin attributes her US success partly to its universal theme and partly to the meticulous translation by Chi-Young Kim.
"I tried to understand and analyse the mother as another human being, the same as all of us, and to portray the burden everyone might have as being a mother to someone else," she said.
"Everyone has a mother, and their mothers have mothers, so I think the sentiment and symbolic meaning behind the mother-figure was commonly shared."
Shin, who is currently on tour to promote her book in the United States, said great effort went into the translation.
"Rather than simplifying Korean backgrounds and words for the sake of foreign readers, my translator, Knopf (the US publisher) and I worked on translating everything word by word," she said.
"Overall, I am very satisfied with the English version."
Unlike in the past, she said, Korea now has competent translators to convey messages effectively in a variety of languages. Interest in the country's literature is growing as more Korean novelists venture overseas.
Kim Young-Ha, another best-seller at home, has published "Your Republic is Calling You" and "I Have the Right to Destroy Myself" in the US.
"Your Republic is Calling You" -- the story of a North Korean spy mysteriously summoned home after 21 years in South Korea -- was the first Korean novel to make Amazon's top 100 literature list.
"Communicating across countries through literature may be hard, but it can also be the tool for the deepest interaction," said Shin, who is also scheduled to publish her latest novel "I'll Be There" in the US.
"I want to see more Korean novels not only in the US but many other countries."