The aim of this research is to determine the organizational commitment levels of the secondary school teachers and administrators. A mixed-method research methodology was used for conducting the research. A census survey was carried out for the quantitative research. However, the sample of the qualitative research was chosen through convenience sampling method. The quantitative data of the research were collected from 401 secondary school teachers and administrators working at public and private schools in the district of Gaziemir located in the province of İzmir in the school year of 2015-2016. The qualitative data of the research were collected from 18 teachers and 6 administrators working at 2 different schools where the quantitative research was carried out as well. The quantitative data of the research were obtained through the “Organizational Commitment Questionnaire” developed by Allen and Meyer (1990) whilst, the qualitative data were obtained through the “Interview Form Related to the Organizational Commitments of the Teachers and Administrators” developed by the researcher. The results of the research can be summarized as follow: Although the organizational commitments of the teachers and administrators are at "Neither Agree Nor Disagree" level, the commitment levels of the administrators are higher than those of the teachers. The organizational commitment component with the highest arithmetic mean is the "Affective Commitment" for both administrators and teachers. The "Normative Commitment" component follows the "Affective Commitment" component. Finally, the organizational commitment component with the lowest arithmetic mean is the "Continuance Commitment". The "Continuance Commitment" levels of the secondary school teachers and administrators working at the same school for 7-9 years are higher than those of the teachers and administrators working at the same school for 4-6 years and for 3 years or less. Again, the "Continuance Commitment" levels of the secondary school teachers and administrators working at the same school for 10 years or more are higher than those of the teachers and administrators working at the same school for 4-6 years. There isn’t a significant difference among the organizational commitment levels of the participants in terms of tenure at school in other components and overall scale. The organizational commitment levels of the participants working as substitute teachers are higher than those of the participants working as permanent and redundant teachers in the "Normative Commitment" component. The organizational commitment levels of the participants, who think that the physical conditions of their school are inadequate, are higher than the others thinking that these conditions are adequate only in the "Continuance Commitment" component. But for the other components and overall scale the situation is reverse. The organizational commitment levels of the participants, who think that the physical conditions of their school are adequate are higher than the others thinking that these conditions are inadequate. The result of the qualitative research has shown that organizational factors are more determinative on the organizational commitment level than personal factors.