Purpose - The purpose of this paper is to determine the relationship between indoor environmental quality (IEQ) and occupants' productivity improvements in green buildings in order to propose probable enhancements of national green certification criteria. Design/methodology/approach - Survey approach was selected under quantitative phenomenon. Hence, questionnaire survey was selected as a primary data collection technique. It was linked to semi-structured interviews to validate survey results. The survey data were analysed by using nonparametric statistical analysis techniques, such as significance testing and Spearman's correlation. Statistical Package for the Social Science (SPSS) v. 20 statistical analysis software was used in data analysis. Findings - Seven factors were identified as significant factors which showed statistically significant monotonic correlation to major IEQ dimensions. Among those, air quality and acoustical partitioning factors confirmed a statistically significant weak positive monotonic correlation, whilst system control showed strongly positive monotonic correlation to occupants' productivity in green buildings. Practical implications - The findings can be practically implied as a basis to review the existing evaluation criteria of IEQ in national green certification system to propose probable enhancements. Originality/value - The significant IEQ factors influencing occupants' productivity were determined as the focal point of this research. Accordingly, new provisions were proposed to enhance the national green certification criteria.