Teaching mathematics entails the use of instructional materials which lead to independent learning. The study evaluated the content validity of a developed worktext in Basic Calculus. The worktext was evaluated/validated by the professor/mathematics teachers in the University and in the Department of Education, and by the students who are currently enrolled in the course Basic Calculus. The study utilized the descriptive-evaluative method in determining the validity of the developed worktext. The respondents were asked to evaluate the worktext using a checklist in terms of its different parts. Moreover, the researchers personally visited some schools for pilot testing of the questionnaire checklist to be used in validating the developed worktext. The reviews led to the refinement of the instrument and minor wording changes. The content validity is very much valid as evaluated by 40 teachers and 40 students and it covers a one whole year in order to finish the worktext and the conduct of the study during the academic year 2020- 2021. This indicates that the respondents strongly agreed that its different parts as to the lesson objectives; lesson inputs, lesson application, and lesson enrichment are useful, appropriate, and very much related to the different topics included in the course Basic Calculus. This further indicates that the validity measures done by the evaluators determine the students’ knowledge, skills, and other attributes. The worktext should be considered as an instructional material and be used in the teaching-learning process of the course. The worktext should be tried out in other school to further improve its effectiveness and practicability.