The factors affecting the mastery of the host country's language by the children of immigrants are important in the study of immigration-related issues. This exploratory study analyses the possible link between parental socio-linguistic background factors (parent-child language choice, parental proficiency in L2, educational level, socio-economic status, and the length of residence in the host country) and the children's social milieu on the one hand and children's lexical knowledge of L2 on the other among Russian-Jewish immigrants to Israel. Participants in the study were 70 Russian-Hebrew speaking children with a mean age of 7 years 2 months and their parents, all Russian-Jewish immigrants in Israel. After investigating the factors that influence Hebrew (L2) vocabulary knowledge, we constructed a composite measure of Hebrew lexical knowledge. In addition, structured questionnaires for parents and children were developed to collect data on target socio-linguistic factors. The findings showed that variability in children's L2 lexical knowledge can be understood, to some extent, by three background factors: parents' educational level, parents' educational experience in the host country, and the length of family residence in the host country. At the same time, the role of parent-child language choice, parental L2 proficiency, and children's social milieu was found to be insignificant. These data are discussed in the context of the distinctive socio-cultural characteristics of the Russian-Jewish immigrant community in Israel. (Contains 4 tables.)