The main purpose of this study is to explore whether, by simply accessing to a new theory, teacher's beliefs and practice will be enhanced. Carl Rogers' (1902-1987) Humanistic Theory was adopted as a case in this study. It highlights whole-person development instead of focusing on intellectual development. A senior high school teacher called Teacher S was selected to participate in this study and the focus was on how she would change after accessing to Rogers' theory. The results showed that large proportion of Teacher S's concerns on teaching focused on academically preparing her students for passing college entrance exam and reacted to Roger's theory with mixed perceptions. After deeply reading Rogers' theory in full-text type, Teacher S became to accept more of that theory and got encouraged due to the consistence between Roger's ideas and some of her innovational ideas such as allowing students to learn at their own pace. The effect of accessing to new theory in this study is no less significant than those found in some longer-time intervention programs (Widden, Mayer-Smith, & Moon, 1998). It was also noticed that Teacher S's acceptance more and more ideas from Rogers was partly due to the consistence between her religious beliefs and some of Roger's ideas.