George Leslie Mackay (1844-1901), the first Presbyterian missionary to northern Taiwan, is considered to be one of the most important persons who influence the development of education and medicine in Taiwan. Recently, the manuscripts written by Mackay which detailed his work from 1871 to 1901 in Taiwan have been computerized and published as Mackays diaries. Researchers who are interested in historical topics concerning religious, educational and medical development in Taiwan hence concentrate their attention on these materials. However, little research applied computational techniques to analyze the content of the diaries. That motivated us to apply text mining techniques to explore the content of diaries. The content analysis methodology was used in this research to unveil the context of Mackays missionary work in northern Taiwan. Finally, the context was presented by data visualization techniques.