Background and aim: Researchers, in qualitative researches, both influences on and take effect from the research process. One of the main issues in qualitative research is validity of the researcher as an instrument of data collection. If the researcher does not have enough validity in the data collection, the results of the study will also not be cited. The researcher as instrument provides an opportunity for researchers to enter into the unknown world of individual about the phenomena in question and sometimes faced many challenges in reaching this goal. This study has been reviewing the opportunities and challenges of researchers as an instrument in the qualitative research.Materials and methods: This was a review study on the methodology of qualitative research. Using keywords including qualitative research, instrument, challenges, and opportunities, articles and available books were investigated in PubMed, Scopus, Science Direct, Proquest, Magiran, SCI, IranDoc, SID, Medlib, IranMedex databases with no time limit. The Quality of the articles was assessed by using the McMaster Critical Review Form for Qualitative studies.Findings: Studies over 12 books and 18 articles showed that the role of the researcher can be varied in different qualitative research designs such as phenomenology researches, grounded theory, ethnography, and content analysis researches.Also previous experience and skills in the process of observation and interview, having effective communication and asking the appropriate questions have an important impact on the role of researchers as a key factor in qualitative research.Conclusions: Researchers have the main role, especially in data gathering of different types of qualitative researches. Actually they are factors that validate the data. Experience and skills, ability to communicate, asking the right questions are the most important factors that have an influence on doing qualitative research in an appropriate ways.