The transition of traditional classroom teaching to online teaching platforms in English as a foreign or second language context has caused the shift of teachers' motivational factors. The present study aimed to develop a new motivational teaching instrument and provide indication for the scale's validity and reliability of English for Specific Purposes (ESP) teachers' basic psychological need fulfillment in online teaching (BPNOT), using samples of Indonesian novice and experienced ESP teachers across genders. The author employed four different development stages of BPNOT's scale using four different independent samples of ESP teachers in Indonesian EFL context (total n = 566). The first developmental stage was designed to develop items for the scale and to establish structure of factorial design utilizing a multivariate statistics of exploratory factor analysis (EFA) test. The second scale development was continued to determine the item scale factorial structure using confirmatory factor analysis (CFA) to confirm whether the construct was consistent or not. The third development stage estimated the test of invariance across gender and teaching experience. Finally, the last developmental stage aimed to revalidate the validity and reliability of the new scale over time. The findings of the preliminary scale validation revealed that the scale has acceptable psychometric features.