Leiba Kaplanowicz was born on 19 April 1919 in Vilnius. His father Donas (?) was from Mikhalishki, not far from Vilnius, his mother was Ida Abewlowicz. From 1930–1936, Leiba attended the coeducational gymnasium Oświata (Enlightenment) of the Vilnius Central Jewish Committee where he showed a talent for languages: he was very good at Yiddish, German, Hebrew, and Polish. In 1940, Leiba applied to the rector of Vilnius University asking to study in the Department of Polish Studies of the Faculty of Humanities. Presumably, he intended to continue studies that he had started elsewhere because the sixth semester is given as the beginning of his studies at Vilnius University. Since he did not have a grade in Latin, Leiba was admitted as an auditor. He passed his Latin examination in November and Leiba was issued a student card. On 19 September 1941, Leiba Kaplanavičius (Kaplanowicz) was expelled from the Philology Department of the Faculty of Humanities of Vilnius University on the basis of the Order of 17 September 1941 of the Higher Education Department of the Board of Education, which was subordinate to the Nazis. He was killed in Vilnius.