Grounded in Social Cognitive Theory and Self-Determination Theory, this study examines the relationship between teacher self-efficacy and motivational teaching styles in the classroom using a sample of 625 Portuguese teachers. Participants completed the Portuguese version of the Situations-in-School (SIS) questionnaire and the Teacher Self-Efficacy Scale in an online survey. Structural equation modeling results showed that teacher self-efficacy is moderately and positively associated with motivating teaching styles (autonomy support and structure) while exhibiting a weaker inverse relationship with demotivating teaching styles (control and chaos). The findings also support the validity and reliability of the Portuguese version of the SIS as an effective tool for assessment and intervention across educational contexts. The discussion highlights the importance of teacher education programs that enhance teacher self-efficacy by targeting its sources while simultaneously promoting the adoption of more effective and engaging instructional approaches. Limitations and directions for future research are proposed.