Suksin Lee was born in P'yŏngannam-do, Korea, the son of I Myŏngse and a woman of the Koksan Kang family.  He earned his medical degree from Kyŏngsŏng Medical College (now Seoul National University) in 1921, and obtained his medical license in August of that year.  After graduation, he studied pathology for several months at Tokyo Imperial University in Japan.  He then traveled to Germany in 1922 to pursue additional studies.
After completing preliminary language instruction and various coursework in chemistry and physiological chemistry at the Friedrich Wilhelm University of Berlin, he earned a doctorate of medicine in 1926.  Lees inaugural dissertation, Ueber Glykolyse', was a study of inorganic phosphates during blood glycolysis. His thesis advisors at the time included Otto Lubarsch of the Chemistry Department at the Pathological Institute, University of Berlin.
While in his final year of studies, Lee obtained a position as a research assistant at a national hospital in Berlin, where he worked until 1927.  During this time he published and co-published several papers on the effects of photosensitive substances on glucose metabolism and cellular respiration.