Yulia Sister was born in 1936 in Chișinău (Russian:  Kishinev), at the time in the Kingdom of Romania, a city which later became the capital of the Moldavian SSR and since 1991 is the capital of Moldova. Her parents and paternal grandparents were also born in this city. The grandparents were there and survived the pogrom of 1903.
David Iosifovich, Yulias father, was a doctor educated in Prague at Charles University. He used to tell his daughter about his student years, the Bessarabian association of fellow-countrymen in Prague and his meetings with famous people. Yulias mother Yevgenia (Bathsheba) Moiseevna copied for her by hand children's verses and Yulia learned to read quite early. Among the first poems was "What Is Good and What Is Bad" by Mayakovsky.
Yulia's grandparents stuck to traditions and spoke Yiddish, and grandfather Yosef (Iosif) even wrote Yiddish poetry. But Yulia could hardly remember them. Her grandfather Moshe (Moisei) died before she was born; her parental grandparents lost their lives in the Kishinev Ghetto in the Holocaust and her grandmother Sarah died during the World War II in evacuation.
During the 2nd World War Bessarabia was reclaimed and then occupied by the Soviet Union in June 1940. A year later in July 1941 it was reconquered by Germany and Romania, and in August 1944 reoccupied by the Soviet Union. In her memoirs Yulia recalled the day when the Red Army entered Kishinev. She also remembered the German bombing of the city and the air raids on the roads, by which her family escaped to the East from the Nazis.
At the beginning of the war David Sister and his family was evacuated to the left bank of the Volga River where he was appointed chief physician at the district hospital and a consultant of the nearby military hospital. The hospital was located in the open steppe between two villages and on the other side of Volga there was Stalingrad. The family lived there a few years. There were no other children in the neighborhood and Yulia had no friends to play with. But she was fascinated by the local nature and made observations of plants and animals. The inhabitants of the hospital could hear the cannonade from the other bank, and during the battle of Stalingrad it became particularly strong.
In 1944 Yulias family moved to Kirovograd where she, after a years delay, was enrolled in the first grade of primary education. A year later the family came back to the native city of Kishinev. Despite severe post-war shortages and difficulties, the Sister's family succeeded to restore their home, which included a huge library. Among the family friends and guests were writers, actors, musicians and scientists, and Yulia grew up in an atmosphere of thirst for knowledge.
Between the years of 1945 and 1954 Yulia Sister studied at the School for Girls Number 2 in Kishinev. Chemistry was taught very passionately by a teacher that loved the subject and was able to convey her enthusiasm to the students. On the advice of her teacher Sister participated in the chemistry enrichment program for school children that was carried out by Professor  at the University of Kishinev.