The purpose of this study is to identify how primary students make decision in an anomalous situation of discrepancy between the observation result and their prior knowledge and what is the relationship between their decision and views on science. In this study, the researchers have observed a science class of fifth graders for two months and collected qualitative data such as field note, audio transcript, video-recording, photo and interviews. It is shown that participants experienced three types of subjective observation as listed: expectation-related, theory-dependent and dilemmatic observation. The questionnaire of the students to the views on science reveals that most of them thought highly of empiricism and utility of science. With this result, it is found that they took into account the limitation and provision of experiments while making judgment in an anomalous situation. That is to say, their assessment of experiments and observation is crucial in judgment in the situation that their observation is incompatible with their prior knowledge. The researchers conclude that their views on science may influence their observation and suggest the ways to promote students' ability linked to observation.