Wireless Sensor Network (WSN) and related technologies are widely used to build decision support systems to solve many real-world problems especially in agricultural environment. Using the basic principles of WSN and Mobile Computing technology, a Smart System for Shiitake Mushroom (SSSM) cultivation in a greenhouse environment was developed near Mount Kinabalu in Sabah, Malaysia. The wireless temperature, humidity and CO₂ sensors are used to collect data in this application. The system monitors sensor data in a feedback cycle where the control devices are activated based on pre-defined threshold values. Implementation of SSSM will optimize the usage of human resources and also maximized the yield of the mushroom.