Background: Having a conscience is one of the main pre-requisite of providing nursing care. The knowledge regarding levels of conscience among nurses in eastern countries is limited. So, the purpose of this study was to examine the level of conscience and its related factors among Iranian oncology nurses. Materials and Methods: This descriptive-correlational study was conducted in 3 hospitals in Tabriz, Iran. Overall, 68 nurses were selected using a non-probability sampling method. The perceptions of conscience questionnaire was used to identify the levels of conscience among nurses. The data were analyzed using SPSS version 13.0. Results: The mean nurses' level of conscience scores was 72.7. In the authority and asset sub-scales nurses acquired higher scores. The mean of nurses' scores in burden and depending on culture sub-scales were the least. Also, there were no statistical relationship between some demographic characteristics of participants and their total score on the perceptions of conscience questionnaire. Conclusions: According to study findings Iranian nurses had high levels of conscience. However, understanding all the factors that affect nurses' perception of conscience requires further studies.