Nature-based tourism, including volunteer tourism on nature projects, is thought to have grown in scale over the past two decades. The personal development of volunteer tourists through their environmental experiences has not been examined in a great deal of research. This paper evaluates this topic for volunteers participating in a small group expedition in Zambia. It investigates over time the personal development of seven volunteers based on their direct experiences of the natural environment, this being examined qualitatively through a series of in-depth interviews conducted with each respondent over the 10 weeks of the expedition. The respondents' direct experiences of the natural environment seem to have affected their personal development both positively and negatively. While motivated to participate in the expedition for conservation, knowledge development and challenge reasons, some expressed mixed views about the environmental tasks they undertook. They felt strong spiritual emotions from being in the natural environment and their self-concept was enriched through both non-environmental and environmental events. The development of social skills also seems to have been important for the expedition experience.