The slow learner characteristics that students have affect their ability to understand specific concepts / information such as understanding the basic concepts of mathematics. This has a negative impact on the failure of students’ vocabulary to slow learning. This study aims to determine the mnemonic keyword strategies in increasing vocabulary acquisition and retention of mathematical vocabulary in students with the slow learner. Mnemonic keywords strategy strategies are strategies that differ between information that will be used for students with information that students already know. Information that has been used by students as a keyword that helps students remember the new information they teach. The study design was a multiple-baseline design on subjects in three slow-learning junior high school students with 12-15 years of income. The intervention given to the subject is in the form of vocabulary prospects with mnemonic keyword strategies. The data chase technique uses a vocabulary assessment with a reliability of 0.849α which measures vocabulary acquisition and vocabulary retention. The research data was determined by determining the results of each research subject and using the Wilcoxon t test statistical analysis. Descriptive results show that the vocabulary of students’ vocabulary and retention of slow mathematical vocabulary can be improved through a mnemonic word intervention strategy. Meanwhile, the results of the analysis show that the mnemonic keyword strategy is effective in increasing the acquisition of vocabulary and the retention of students’ vocabulary with the slow learner. The implication is that this research can be the basis for developing more complex slow student mathematics.