This study entitled Out-of-Field Specialization Teaching focused on teachers teaching out-of-field of specialization subjects. This research sought to determine the concerns and challenges of teachers teaching out-of-field of specialization in Nueva Ecija High School. The researcher utilized the descriptive method of research to aid the study and the purposive sampling technique in the gathering of data. This study was conducted to 30 respondents from Nueva Ecija High School where all are teachers handling different subjects. Results revealed that those teachers who are teaching out-of-field subjects have performed satisfactorily specifically in terms of the following; mastery of the subject matter, teaching strategies and methodologies and management of learning. It also appeared in this study that they less often experienced difficulties in mastering their subject matter. They never encountered problems relating to teaching. Competencies of teachers are upgraded through seminars and trainings that they have attended. Based on the results, the researchers recommend the following: the school administrators may upgrade the competencies of their teachers in the form of seminars, trainings, scholarships and other forms of retooling activities specifically for teachers who teach out-of-field of specialization subjects. Priority be given to those teachers who need to be retrained, while stipends may be provided to those mentor who will assist those new recruits in the field. A similar study can be conducted in other schools or divisions to come up with more data and should involve students for better understanding the impact of out-of-field teaching to learning.