This study aims (1) to develop an instructional model to enhance mathematical literacy for secondary students and (2) to examine the effects of using this instructional model. The sample group consisted of students from Lampabpla Wittayakarn School, under the jurisdiction of the Surin Secondary Educational Service Area Office in Thailand by using cluster random sampling, during the second semester of the 2021 academic year. Fifteen students from Grade 9/2 were selected as the experimental group, and 15 students from Grade 9/1 were selected as the control group. The data collection tools: 1) interviews; 2) focus group discussion; 3) mathematical literacy tests; and 4) student satisfaction questionnaires. The statistics used for data analysis include percentage, arithmetic mean, standard deviation, dependent and independent t-test. The research findings revealed that (1) the instructional model to enhance mathematical literacy for secondary students comprises six components: 1) principles and basic theoretical concepts, 2) objectives of the model, 3) instructional management procedures, 4) social system, 5) principles of response, and 6) support system. (2) results of using the instructional model showed that: 1) the experimental group of students had markedly higher mathematical literacy after the intervention compared to before, at the 0.05 significance level; 2) the experimental group had significantly higher mathematical literacy than the control group, at the 0.05 significance level; and 3) the experimental group reported the highest level of satisfaction with the instructional model to enhance mathematical literacy for secondary students, with an average score of 4.50 and a standard deviation of 0.17.