The purpose of the study was to assess the effects of ecology-based nature education program on elementary school students' environmental knowledge, environmental affect, and responsible environmental behavior. A total number of 64 elementary school students including 26 females and 38 males who participated in summer natural education organized in Ankara in 2008 and supported by TUBITAK was the sample of this study which was designed as pretest- posttest experimental study. A series of data collection instruments was administrated to the sample at the beginning and at the end to assess students' knowledge, affect, and behavior regarding to environment. Qualitative data were subjected to content analysis whereas quantitative data were analyzed using repeated measures of ANCOVA and t-test. This study showed that ecology-based nature education program contributed significantly to children's responsible environmental behavior. Although students' posttest environmental knowledge and affect scores were higher than those of pretest scores, no significant effect of nature education program on environmental knowledge and affect were observed. (Contains 1 table.)