Objective: This study was carried out to develop an instrument to measure the emotional well-being of mothers in line with the Deck-Chair theory of Jean Ball. Design: Scale development and psychometric testing study. Setting: Turkey Population or Sample: A total of 398 postpartum women were included. Methods: MEWBS was administered to postpartum women being prepared for discharge (n=398). Factor analyses were carried out to determine the construct validity of the scale. Cronbach’s alpha coefficient was used to assess the reliability of the scale. Main Outcome Measures: MEWBS is a valid and reliable scale. Results: KMO value for EFA was found to be 0.806. As a result of the factor analysis that was carried out with the varimax orthogonal rotation technique, three factors explaining 51.825% of the total variance in the measured characteristic (Healthcare and Education, Social Support, and Mother’s Personality and Experiences) were identified. The internal consistency coefficient of the scale revealed that it was highly reliable (Cronbach’s alpha=0.860). It was determined that the scale did not have response bias (Hotelling’s T ²=397.260, p=0.000), and its factors were additive (non-additivity: 0.000). Conclusion: The validity and reliability test results of MEWBS demonstrated that it is a valid and reliable measurement instrument to assess the emotional well-being of postpartum mothers being prepared for discharge. MEWBS can guide healthcare professionals in identifying the emotional well-being of mothers in line with Jean Ball’s deck-chair theory and providing care accordingly. Therefore, healthcare professionals are advised to use MEWBS in their routine practices and assessments of mothers.