During the Sino-Japanese War, Sano served as the chief of staff of the 14th Division in northern China from 1937 to 1938. Promoted to major general in 1938, he took command of the 4th Field Heavy Artillery Brigade. In 1940, he was director of the Field Artillery School.
At the beginning of the Pacific war, Sano was a lieutenant general and commander of the 38th Division. His division captured Hong Kong in December 1941 and assisted in the capture of Sumatra in the Netherlands East Indies in February 1942. Sent with his division to Guadalcanal in October 1942, Sano and his unit were evacuated in February 1943. Appointed chief of staff of the Homeland Defense General Headquarters, Sano commanded the Thirty-Fourth Army in central China in 1944 and 1945, where he engaged in the defense of Wuchang and Hankou (Hankow), both in Hubei (Hupeh) province. He was assigned to the China Expeditionary Army Headquarters in 1945 and died of illness on 3 July 1945.
Carew, Tim. The Fall of Hong Kong. London: Blond, 1960.; Frank, Richard B. Guadalcanal: The Definitive Account of the Landmark Battle. New York: Penguin, 1990.