An institutional Review Board (IRB) is a committee of people of different professions and the lay. The task of IRB is to review and evaluate research proposals involving human subjects with respect to the scientific soundness and ethical acceptability. Although several studies have emphasized the importance of conducting scientifically and ethically sound research in a quality scientific and ethical conduct there were reasons to believe that shortcomings in proposals submitted to CRERC exist. Experience shows some proposals are rejected outright or some are accepted with minor and major corrections. This means that shortcomings exist in adherence to CRERC guidelines and other IRB standards. Objective: The study aimed at assessing the scientific and ethical quality of research proposals submitted to CRERC for review in the light of methodological and ethical aspects of the research proposals requirements from 2001 to 2009. Materials and Methods: A retrospective document review of the all research proposals that were submitted for review to CRERC from 2001 to 2009. Quantitative data was obtained through a checklist which assessed the presence or absence of a methodological or ethical parameter of interest so as to obtain the quality of assessed research proposals and qualitative data was obtain by in depth interview of CRERC members. Quantitative data was analysed by the help of SPSS version 13.0 software programme which used both quantitative and qualitative research methods and Qualitative data was analysed manually using thematic framework analysis. Setting: The study was conducted at Research Ethics and Review Committee (CRERC) office at Kilimanjaro Christian Medical College. Results: Of 150 research proposals assessed 69.3% were basic research. 62.0% used quantitative research methods. More than one thirds of the research proposals assessed (34.0%) were cross sectional studies followed by randomized study design 29.3%.The leading themes in the research proposals that were assessed was HIV (38%), followed by Malaria (12.7%) then Tuberculosis (10.7%). Only 25.3% of all research proposals assessed were of good quality with respect to the total methodological aspect score and (36.7%) of all research proposals assessed were of good quality ethical quality with respect to the total ethical aspects scores. Conclusion: The findings indicated that majority of research proposals assessed were on HIV by themes, quantitative research methods and cross sectional study design were mostly preferred by researchers and the scientific quality of most research proposals with respect to methodological aspects was generally of poor quality and the ethical quality with respected to the ethical aspects in the research proposals was of good quality. Half of research proposals with good methodological quality were also found to have good ethical quality and vice versa.