In August 1933, after Hitler came to power, Dubnow moved to Riga, Latvia. He chose Latvia in part for its government's support for Jewish self-reliance and the vigorous Jewish community in the small country. There existed a Jewish theater, various Jewish newspapers, and a network of Yiddish-language schools. There his wife died, yet he continued his activities, writing his autobiography "Book of My Life", and participating in YIVO, the Institute for Jewish Research. On the initiative of a Latvian Jewish refugee activist in Stockholm and with help from the local Jewish community in Sweden, Dubnow was granted a visa to Sweden in the summer of 1940 but for unknown reasons he never used it. Then in July 1941 Nazi troops occupied Riga. Dubnow was evicted, losing his entire library. With thousands of Jews, he was transferred to the Riga ghetto. According to the few remaining survivors, Dubnow repeated to ghetto inhabitants: "Yidn, shraybt un farshraybt" (, write and record"). He was among thousands of Jews to be rounded up there for the Rumbula massacre. Too sick to travel to the forest, he was murdered in the city on 8 December 1941. Several friends then buried Simon Dubnow in the old cemetery of the Riga ghetto.