This study is to investigate the correlation between language aptitude and vocabulary levels of 5th graders of a Korean elementary school. The participants of the study were 39 elementary school students in Daejeon Metropolitan City. Language aptitude was elicited using LLAMA B, D, E and F classified respectively into memory retention, sound recognition, sound-symbol correspondence, and inference and application. A vocabulary size test modified from the vocabulary size test (Nation, 1990) was injected to the students to investigate their vocabulary levels. A correlation between each LLAMA score and vocabulary size of students was tabulated for their correlationship along with their statistical significance of 95% probability rate. The findings are: Positive correlations were found between each language aptitude ability and vocabulary ability. Among them, the correlation between memory retention and vocabulary ability is only statistically significant. This finding implicates that memory retention is an important factor to learn and retain new words, and learning vocabulary with pictures is recommended to reinforce the connection between meanings and forms of new words.