This study tries to investigate the trends of change and its causes through time-series analysis beyond the limit of cross-section analysis. Two questions are set up for this purpose. First, what is the level of university’s efficiency? Second, how university’s efficiency has changed? The first research question of university’s efficiency results are as follows; as examining the overall efficiency level of Korean universities, it is found that approximately 7~11% of universities work efficiently whereas other 73~83% work inefficiently. The second research question of the efficiency analysis by year is as follows; according to the assessment result of input and output variables of this study, university’s efficiency is quite low generally. However, it seems to change positively because the values of the efficiency and the values of input and output variables by year tend to increase as a whole. The analysis result of the efficiency between efficient universities and inefficient universities is commonly consistent to some extent by year. It is found that there are 5 universities which continuously maintain high efficiency for five years. It is also found that there are 3 universities which are steadily included in the lowest group. These universities need to increase the level of input and the output in general.