Effective communication is one critical characteristics of effective and successful school principal. Research on effective schools and instructional leadership emphasizes the impact of principal leadership on creating safe and secure learning environment and positive nurturing school climate. This paper was designed to study the relationship between effective communication of high school principal's and school climate. Two instruments were used to measure school climate and communication effectiveness between principals and teachers. Participants were 555 students (293 males and 262 females) and 208 teachers (107 males and 208 females) from Abu Dhabi District, UAE. Results indicated that school climate is positively associated with principal's communication effectiveness. Better climate school was expected in schools where effective communication between school principal and his/her teachers exists. In addition, schools were found to be different in their principal's communication effectiveness and on their climate especially on Security and Maintenance and Instructional Management. Significant differences were also observed between males and females for the advantages of female schools on Security and Maintenance, Student Behavioral Values, Student-Peer Relationships, and Instructional Management. On the other hand, communication between principals and teachers in male schools was more effective than that in female schools. The following are appended: (1) School Climate Survey; and (2) High School Principal's Communication Survey. (Contains 2 tables.)