Project effectiveness is a challenge in sustainable building construction projects. Lack of experience, knowledge, and skills in sustainable projects have been highlighted as the main barriers to using sophisticated and innovative techniques. Based on the literature, the pre-project planning effort directly influences a project's success. Nevertheless, the differences in planning efforts for green projects have not been fully determined, especially in Thailand, where sustainability just has only recently been considered in this context. This study investigated the status of pre-project planning for green building construction projects located in Thailand to promote sustainable construction. The analyses were performed based on two main objectives: (1) to compare the overall planning effort and (2) to address dissimilar planning factors between green and conventional projects. The concept of a project definition rating index (PDRI) was applied to evaluate the level of pre-project planning effort in 42 sample projects. An independent t-test was used for data analysis. The findings can contribute as the key strategies to facilitate the planning for sustainable buildings and help new practitioners to effectively allocate their constrained resources on significant project activities during the implementation of sustainable building construction.