Due to the growing insurgency and increase in crime rate in the country, provision of adequate and functional streetlights as one of the security measures have become necessary in Nigeria for the protection of life and property. In this study, we designed and constructed an Automatic Streetlight Controller using a Microcontroller and Light dependent resistor (LDR). The Microcontroller was programmed using Arduino C language and simulated using Proteus 8.0. The prototype of the circuit was constructed by soldering the components permanently on a Vero Board according to the design specification. The device was tested for proper functioning and optimum performance. Results show that on testing the device for Specificity, Response Time and Accuracy gives 96.77%, 0.02sec and 96.67% respectively. The device can be of great importance if implanted in existing street lights or newly built ones so as to improve the condition of our street lights to proper illuminate our streets for an improve security system.