The objective of the research was to determine the correlation between reasoning, and emotional intelligence in social interaction to mathematics achievement. The research was conducted at SMP 5 Yogyakarta, Indonesia with 90 respondents who were selected by random sampling. The research verified the hypothesis used a survey method with correlation and regression technique approach. The research involved 3 (three) variables such as; mathematics achievement as the dependent variable and two other variables as the independent variables. They were reasoning and emotional intelligence in social interaction. The study found that there was a positive correlation between (a) reasoning and mathematics achievement; (b) emotional intelligence in social interaction and mathematics achievement; and (c) there was a positive correlation between reasoning and emotional intelligence in the social interaction to mathematics achievement. This study is expected to be a consideration for developing mathematical achievement through student reasoning, developing mathematical achievement through emotional intelligence in social interactions, and developing mathematical achievement through reasoning and emotional intelligence in social interactions.