The study ascertained the relationship of the Big Five Personality Factors (openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism) and job performance among 180 randomly selected private and public elementary, secondary, and higher education teachers in Iloilo City, School Year 2009-2010. The quantitative data were obtained using the Big Five Inventory and the Job Performance Rating Scale. Six informants supplied the qualitative data with the use of in-depth interviews. The descriptive statistics employed were the freuency count, SD, and mean; the inferential statistics were the t-test, One-way Analysis of Variance (ANOVA), Pearsons r, and stepwise multiple linear regression set at .05 alpha. The findings of the study showed that as an entire group, the teachers exhibited high levels of openness to experience and conscientiousness and very high in agreeableness. They showed an average level of extraversion but low neuroticism. The teachers job performance was very satisfactory. Likewise, the study also revealed that the higher the teachers level of openness to experience, conscientiousness, extraversion, and agreeableness, the better was their job performance. Conversely, the lower the level of neuroticism, the higher was the job performance. Furthermore, there were significant differences in the teachers openness to experience, consciousness, extraversion, and neuroticism when classified acoording to sex, civil status, educational qualification, length of service, teaching assignment, and type of school. Similarly, there was a significant difference in the job performance of conscientious teahers in favor of those who had very high level of conscientiousness. The teachers job performance did not differ significantly when classified according to their openness to experience, extraversion, agreeableness, and neuroticism. Thus, among the Big Five Personality Factors, only conscientiousness and agreeableness were positively and significantly related to job performance. And only conscientiousness was found to be a significant predictor of job performance. Correspondingly, the identified personality factors were exemplified by the informants, confirming the influence of these traits in the performance of their work.