The study aimed to develop and validate learning module on exponential and logarithmic functions based on the Understanding by Design lesson plan. The study was descriptive in nature, describing the instructional materials and its properties. The research flow was based on the works of Emily K. Dunsker in 2005 and the suggested procedure on formative evaluation by Talisayon and Vistro-Yu. Purposive sampling technique was used in determining the respondents. Respondents involved selected mathematics experts and grade 11 students. They were responsible for evaluating the module. Feedbacks of expert had served as guide in the module revision. Student respondents were involved in the formative evaluation. A word-sentence list forms were given to students to identify difficult or vague words, phrases and sentences as they read the module carefully. The module was subjected to readability test to determine the student involvement index, communication index and the grade level of the module. The study showed that the module has high involvement index, the communication index fell out of the acceptable range and the module level was college. These results called for another revision with complete change in structure and mode of presentation but still based on the Understanding by Design lesson plan. The study recommended to revised module and to subject it to readability test again to ensure that the module would be appropriate to the users. A summative evaluation is also recommended to determine its effectiveness.