The study probed on the effects of integrating learning portfolios in Mathematics on the 21st-century learning skills of Grade 8 learners. It was conducted in Pangantucan National High School, Pangantucan Bukidnon during the second grading period of the school year 2018-2019. A quasi-experimental pretest-posttest research design was used with two-intact classes. The participants of this study were sixty (60) Grade 8 learners. Thirty (30) learners from the experimental group were matched with thirty (30) learners from the control group, based on their first grading performance in math, and gender. Four research instruments were used in the study. The Critical Thinking Skills Test, Collaboration Survey Questionnaire, and Mathematical Creativity Skills were researcher-made tests that measured critical thinking skills, collaboration skills, and creative problem-solving skills, respectively. The Written Communication Rubric for Mathematics, adopted from Quasar Mathematics General Rubrics, was used to measure written mathematical communication skills. The data were treated with One-way Analysis of Covariance (ANCOVA) at 0.05 significance level. The study revealed that there were significant differences in the performance of grade 8 mathematics learners on critical thinking, communication, collaboration, and creativity when taught using learning portfolio and conventional forms of teaching strategies in favor of the experimental group. Therefore, the use of a learning portfolio in mathematics is effective in enhancing the 21st-century learning skills of grade 8 learners.