This paper, titled, “Design of Microcontroller-Based Intelligent Street Light Controller” uses AT89C52 microcontroller as its controlling device. The system switches on street lights at night and turns them off once darkness disappears in the morning. In this paper, an algorithm was developed for the system of operation, and the control program was written from the algorithm in Assembly language; though it could be written in any embedded system programming language like Embedded C++. The choice of any light-controlled sensor is possible but this research work uses Light Dependent Resistor (LDR) as its sensor for monitoring application. Real-time simulation was done using Proteus software so as to ascertain the workability of the design in real life. A prototype of the system was implemented and it tested ok.