This research aimed to investigate the factors and indicators of quality culture for secondary school with extra-large school size in the northeast region of Thailand. The researchers employed a mixed-mode design. They conceptualized quality culture factors and indicators by analyzing documents and previous studies, followed by a survey of 380 respondents with the purpose of testing the goodness of fit of the identified factors and indicators of quality culture with the empirical data. The findings revealed a total of 14 indicators derived from the five factors in a quality culture model and they were found parallel to the empirical data.