The effects of material monitoring and information sources of maternal knowledge on externalizing and internalizing behaviors of adolescents were examined with a sample of 323 ninth-grade middle school students(163 boys and 160 girls) and their mothers. Data were collected using questionnaires regarding maternal monitoring, information sources of maternal knowledge, and externalizing and internalizing behaviors of adolescents. The major findings were that 1) unemployed mothers showed more monitoring than employed mothers; 2) mothers perceived that girls showed more self-disclosure and were more controlled by them than boys; 3) girls showed more internalizing behavior than boys; 4) the more adolescents were monitored by their mothers, the less internalizing behavior they showed; 5) the more maternal solicitation was used, the more externalizing behavior girls showed; 6) adolescents showed the least externalizing behavior when maternal monitoring was highly perceived by both mothers and adolescents. And perception of maternal monitoring by adolescents themselves plays an important role in showing less externalizing behavior.