The book was met with a generally positive reception. Writing for The New York Times, literary critic Michiko Kakutani stated "though the book is flawed by a bluntly didactic conclusion, the earlier pages testify to the author's lyric gifts and narrative poise". Sylvia Santiago of Herizons magazine described Otsuka's writing style as "scrupulously unsentimental", thus "creating a contrast to the sensitive subject matter". O: The Oprah Magazine said the novel was "a meditation on what it means to be loyal to one's country and to one's self, and on the cost and the necessity of remaining brave and human".
When the Emperor was Divine won the American Library Association's Alex Award in 2003 and also won an Asian American Literary Award.