Background: In addition to phonological processing and vocabulary, morphological awareness has been clearly identified as contributing to learning to read. While the impact of socio-economic status (SES) has been identified for both phonological processing and vocabulary, less is known about the SES influence on morphological awareness and its relationship to reading achievement. The study had two aims: to assess the net effect of SES on morphological awareness and to compare the independent contribution of morphological awareness to reading scores as a function of children's SES (middle vs low SES) when phonological processing and vocabulary are held constant. Methods: The sample included 162 French third graders from low-SES and middle-SES schools. Children were assessed on reading-related and literacy tests (phonological processing, vocabulary, morphological awareness, reading accuracy, fluency and comprehension). Results: First, while morphological awareness was lower for low-SES children, regression analyses showed that SES did not explain the morphological awareness score when phonological processing and vocabulary were taken into account. Second, while the morphological awareness contribution to reading accuracy did not differ across SES, its contribution to reading fluency was weaker in low-SES as compared to middle-SES children. Only vocabulary score predicted reading comprehension in low-SES. Interestingly, morphological awareness was stronger than vocabulary as a determinant of reading scores in middle-SES children, while it seems more dissociated from vocabulary in accounting for reading scores in low-SES children. Conclusions: The contribution of morphological awareness to low-SES children's reading scores opens possibilities for morphological awareness-based interventional studies in children with narrower vocabulary skills.