This study was undertaken to investigate the relationship between critical thinking tendency, academic optimism, and teaching philosophy among senior secondary school teachers. The research design was descriptive-correlational and random stratified sampling method was utilized to draw the sample (114 subjects). The research instruments consisted of Critical Thinking Disposition Questionnaire (Ricketts, 2003), Academic Optimism Scale (Beard et al., 2010), and Educational Philosophy Survey (Sadker & Sadker, 1997) whose validity and reliability were confirmed. The collected data were analyzed using Pearson correlation coefficient and multivariate regression. Results demonstrated that there was a positive, significant relationship between the efficiency dimension of the component of academic optimism and educational philosophies of Perennialism, Progressivism, and Reconstructionism, and between the dimension of trust in parents and students and educational philosophies of Essentialism, Perennialism, Progressivism, and Existentialism, as well as between the dimension of academic emphasis and educational philosophies of Progressivism and Reconstructionism. Furthermore, it was found that there was a positive, significant relationship between innovativeness component of critical thinking tendency and educational philosophies of Perennialism,  Progressivism, and Reconstructionism, and between the dimension of cognitive maturity and educational philosophies of Essentialism, Perennialism, and Existentialism, as well as between the engagement dimension of commitment from the component of critical thinking tendency and educational philosophies of Essentialism, Perennialism, Progressivism, Reconstructionism, and Existentialism. Based on the findings, the share of the components of commitment (0.40) and trust in parents and students (0.260) was more than other components of critical thinking tendency and academic optimism in the explanation of the philosophies of education.