Environmental Education (EE) has been recognized by international community as response to environmental concerns and problems (mainly induced by human activities) to be integrated into their respective educational systems. Accordingly Ethiopia considered EE in its policy and strived to incorporate environmental components into all school subjects. In spite of policy provision and efforts of integrating EE components into all primary school subjects, currently environmental problems and crises are getting diverse and complex. Proper understanding of environment, issues, and its systems, human-environment interrelationship, as well as developments of a sense of environmental concern and caring behavior are visibly lacking. This study was intended to investigate the integration of EE into all subjects of Ethiopian Primary Schools as indentified from primary education curricular document-textbook, and perceived and practiced by primary school teachers. The study was supported by ideas and views obtained from international and national literature review, particularly underpinned by EE integrative model of Palmer (1998). Qualitative case study method was employed to generate empirical evidence, where four primary schools were purposely selected and included in the study. The data were obtained from 16 textbooks reviewed, 22 primary school teachers’ interviewed, and 5 lessons observed. The first two sources were identified using purposive samplings while the last via convenient sampling. The result revealed that EE as currently planned and taught in primary school curriculum is not sufficiently integrated into all primary school subjects as intended. The finding confirmed that though EE is believed to be integrated into every subject of the school curriculum its integration found to be different in coverage and approach by subjects and cycle. It is only sufficiently integrated into science subjects notably biology and geography from social studies mainly based on the matching of these subjects contents with the EE contents. It was also found that EE components waere integrated and taught in education about the environment mode than balancing with education in and for the environment perspectives. The findings of the study further disclosed inconsistence between integration of EE at curriculum level and the practice of integration at teaching, lack of clear criteria and facilitating body for the integration of EE components into all subjects was reported as barriers among others. Rigid teaching approach, (manifested in form of textbook confined, classroom limited, teacher controlled methods and rare use of examples fromreal environment) was also noted as limiting factor. Thus, the finding suggests EE as presently designed and taught is constrained to lead to the attainment of environmentally literate, concerned and responsible citizen. Subsequently, this study seeks to reinforce EE and its integration into all school subjects and its actual integration at learning level. It is also suggested the related actors’ notably educational theorists’, educators, policy makers and curriculum developers and teachers to review and rework their roles to respond to the gaps implied. In conclusion the study proposes a modified integrative EE model to be considered for mainstreaming and teaching EE components in primary school subjects. Key Words Environment, sustainability, environmental education, integration, integrated curriculum, education about, in and for the environment