Background: Preconception care (PCC) is highly recommended evidence-based intervention to optimize women’s health in particular and in so doing reduce the incidences of adverse pregnancy outcomes (APO). PCC targets modification of risk factors to APO occurring before and just at early weeks of conception. Nevertheless, in Ethiopia, the need to implement PCC as part of the continuums of the comprehensive Maternal, Neonatal and Child Health Care services is not yet studied. Purpose/Aim of the study: This study aimed to develop a guideline to assist the incorporation of PCC in Ethiopian health system thereby reduce the highly incident APOs in the country, which is the purpose of the study. Methodology: This study applied the explanatory sequential mixed method to determine the determinants to the non-implementation PCC in Ethiopia. In addition, a policy document analysis was conducted to identify the existence of policy guiding the implementation of PCC in Ethiopia. Finally, the study applied a Delphi technique to increase the utility and acceptance of the guideline developed. The study was guided by a theory based framework called a Framework for Determinants of Innovation Processes (FDOIP). RESULT: Nearly all (84.7%) of the healthcare providers (HCPs) never ever practiced PCC. Even among those who ever practiced, the majority (74%), practiced it poorly. More than two third (68.6%) had poor PCC knowledge. HCP’s with good PCC knowledge had likely hood of practicing PCC by four times greater than those with poor PCC knowledge (AOR=4.4, 95% CI: 2.5-7.6). The policy document analysis identified the absence of policy guiding the practice of PCC in Ethiopia. The HCP’s curriculums also didn’t include PCC. The determinants to non-implementation of PCC, as perceived by the qualitative study participants include absence of national PCC policy , absence of PCC guideline, lack of institutional PCC plan, presence of other competing demand, lack of laboratory facilities and setup, lack of accountable body, absence of Individual or organization introduced PCC to the country, absence of trained manpower on PCC, absence of known expert in PCC, Poor public awareness about preconception health and PCC, Unplanned Pregnancy and poor health seeking behaviour. CONCLUSION The study revealed the absence of a standard and complete PCC practices by the HCPs. Nearly all HCPs never ever implement PCC. Even those very few practitioners were found practicing PCC poorly that is in a substandard, incidental, and in an inconsistent way. There is no formal policy document guiding the implementation of in Ethiopia. The HCPs training curriculum didn’t include PCC. The guideline developed base on the study findings of the study recommended to incorporating PCC in Ethiopia health system. / Health Studies / D. Litt. et Phil. (Health Studies)