—Since the Covid 19 Pandemic by the end of 2020, the learning process has shifted from school to online home-based- learning. Several technologies are applied for enabling students’ participation. Technology-based learning needs to be designed to be attractive and integrated with local culture. The present study developed a valid, practical, and effective Sasak ethnomathematics-based e-Module. The e-Module was mainly designed to improve students’ metacognitive abilities. The study used development research using a 4D development model consisting of four categories: defining, designing, developing, and disseminating. The research was conducted in one of the elementary schools in West Lombok. Ten students of grade five and 30 students of grade six were selected for large-scale trials. The validity test showed that the ethnomathematics-based- e-Module was highly feasible to be used as a learning resource with an average score of 3.65. The questionnaire’s analysis of students’ responses showed that the e-Module fell into the practical category with a practicality percentage of 89%. The results of data analysis using independent sample T-Test showed that the T-test value was 0.00 < 0.05, thus the results of the study revealed a significant difference. Overall, the ethnomathematics-based- e-Module was valid, practical, and effective for improving students’ metacognitive abilities on spatial material. The students can access the e-Module via smartphones or laptops, allowing them to remotely without time restrictions.