The adoption of the 1/2S d/2 tapping system by rubber smallholders is far behind the expectation of the Rubber Research Institute of Sri Lanka in Moneragala District. This study has assessed the behavioral factors that influence the adoption of the 1/2S d/2 tapping system. Data were collected using stratified random sampling. A self-administrated survey was deployed among rubber smallholders (self-tappers) in Moneragala District during 2020. The conceptual model was developed based on the decomposed theory of planned behavior. Study variables were measured using validated research instruments. A two-stage model-building process was applied. The conceptualized model was tested empirically, using partial least square structural equation modeling (SMART- PLS 3.2 version). The composite six-predictor conceptual framework and structural model explained 79% of the variance in the adoption of the 1/2S d/2 tapping system by rubber smallholders. The adoption of 1/2S d/2 by rubber smallholders positively correlated with the behavioral factors, behavioral intention, and perceived behavioral control. There were positive relationships between; compatibility and attitude, relative advantage and attitude, perceived usefulness and attitude, perceived ease of use and attitude, subjective norms and behavioral intention, facilitating condition, and perceived behavioral control. These findings can help boost the behavioral intention of rubber smallholders in Moneragala District in using 1/2S d/2, especially by improving the aspects of attitude and subjective norms of tappers.