This study aims to explore the relationship between teacher's professional growth and teaching effectiveness of public preschool teachers in Tainan City. The study uses questionnaire to collect data regarding preschool teachers' professional growth and teaching effectiveness. By cluster sampling, a total of 306 questionnaires are distributed, and 275 effective ones are retrieved. Based on study results, some findings are obtained: the present statuses of the public preschool teachers' professional growth and teaching effectiveness in Tainan City are in good condition; significant differences on preschool teachers' professional growth vary with different preschool scale, teachers' teaching years and age; significant differences on preschool teachers' teaching effectiveness vary with different preschool scale, teachers' age and educational level; preschool teachers' professional growth has high predictive power on teaching effectiveness. Finally, according to conclusions, some suggestions are offered to educational administrative organization, preschool, preschool teacher and future research.