The psychrometric parameter, Relative Humidity (RH), plays a key role in maintaining the greenhouse environment, where RH must be necessarily within the range of 60% RH to 80% RH. The investigators have presented various processorbased electronic systems as well as embedded systems based on microcontrollers for monitoring and controlling the Relative Humidity (RH) of greenhouse environments. It was also found that precise and reliable embedded systems are in great need. Therefore, an attempt is made to design and develop an advanced microcontroller—the Advanced Virtual Reduced Instruction Set Computer (AVR)—based monitoring and controlling system for relative humidity. AVR's ATmega8 is an 8-bit tiny computer on a chip. It has Reduced Instruction Set Computer (RISC)-Harvard architecture, so it has more promising features—low power consumption, six sleep modes, an inbuilt Analog to Digital Converter (ADC), fast serial communication, a programmable watchdog timer with a separate on-chip oscillator, etc.—than those of other microcontrollers. The RH-dependent data is sensed by the precise temperature-compensated sensor module, SY-HS- 220, which is capacitive type and exhibits a current consumption of less than 3 mA. The digital readout is ensured by a smart 16x2 Liquid Crystal Display (LCD) module. The relay circuits are wired to maintain the humidity within the prescribed range by deploying a cooling fan and fogger. The firmware is developed in embedded C using the Code Vision AVR Integrated Development Environment (IDE). This embedded system under investigation is calibrated and standardised to a scientific unit, relative humidity (RH%). The complete development, implementation, and results of the system under investigation are depicted in this paper.