The purpose of this study is to develop a Computerized Ecology Observation Competence Assessment (CEOCA) to investigate the characteristics of students’ observation competence. The authors assume that the students’ observation competence can be enriched by meaningful experiences and the performance is situated in specific content or context. The facets included in CEOCA are knowledge, observation (on multi-media), concept mapping of wetland ecology. A total of 454 6th, and 7th graders were sampled in this study. The average difficulty (p value) is .62 for the sample. The correlation coefficients between CEOCA and related variables such as school math or science score are around .46 to .54. The pattern of correlation coefficients demonstrates sensible supporting evidences for the convergent and discriminant validity. The implications for further researches are also discussed.