The aim of this research is to determine the validity of the expert assessor's responses to the Pancasila Student Character Learning Environment Inventory instrument at the Senior High School level. This research uses quantitative methodology with a survey method, while a sample of 20 panelists was selected using purposive sampling from students who have completed their PEP Doctoral education and students who are currently completing their Doctoral education. Data collection through the non-test form of the Pancasila student character learning environment inventory instrument was distributed with the help of Google Form. Interrater reliability uses Intraclass Correlation Coefficients (ICC), the results of the analysis show a value of 0.77, which means good reliability. Data analysis uses the Aiken formula technique to analyze the validity of the expert assessor's response results. The results show that the instrument, which was designed from six dimensions, 19 indicators and 53 items, has a validity value in the range of 0.46 to 0.91 in the adequate category. Meanwhile, the dimension with the greatest validity value is the global diversity dimension with a validity value of 0.81 and the smallest validity value is the critical reasoning dimension with a validity value of 0.73. The panelists' suggestions and recommendations are that the items in each indicator be developed and adapted to the construct of the instrument being developed.