This qualitative case study explores the decision-making process of administrative staff in a private senior high school when they face an ethical dilemma, aiming to discover the beliefs and principles applied when the staff make decisions and the factors that underlie those decisions. In the study, semi-structured interviews were conducted to ten administrative staff at the positions of division director and sub-division chief in a senior high school in New Taipei City. The summarized findings are as follows: 1. Ethical dilemmas being constantly faced by administrative staff in the private high school are: 1) conflict of beliefs; 2) human relations versus system; 3) difficulties in interpreting roles; and 4) struggle between ideal and reality. 2. Steps of a decision-making process for administrative staff in the private high school are: 1) determine the nature of the dilemma; 2) make sure the right objective; 3) gather extensive information; 4) study feasible solutions; 5) evaluate the scope of influence and outcomes for each solution; 6) select the best solution; 7) execute the solution; and 8) review and adjust the solution. However, interviewees who discuss the decision-making process are mostly division¡¦s directors, while sub-division chiefs tend to ¡§take orders¡¨ from above and seldom have the opportunities to decide the steps during the decision-making process. 3. Beliefs held by the administrative staff during a decision-making process for an ethical dilemma are: 1) protect students¡¦ rights and interests; 2) maintain fairness and justice; 3) communication with rational respect; 4) commitment in the administrative professionalism; and 5) establish a mutual objective. 4. Principles applied by the administrative staff during a decision-making process while facing an ethical dilemma are: 1) solve the dilemma fairly; 2) communicate genuinely; 3) keep open mind; 4) behave following regulations; 5) act professionally; 6) respect and empathize; and 7) follow instructions from above. 5. Factors that affect the administrative staff¡¦s decision-making process for an ethical dilemma can be divided into two categories: 1) internal and personal factors; and 2) external and circumstantial factors. Based on research findings, the study suggests the administrative staff in the private senior high school to adopt the following practice in order to reduce ethical dilemmas: 1) to make sure the school¡¦s directions and its educational objectives; 2) to acquire consensus among organizational members through frequent communication; 3) cultivate respect, trust, and a harmonious environment; 4) nurture organizational members to increase their professional capacity and to stimulate creative thinking. Keywords: ethical dilemma, decision making, decision-making process, administrative staff¡¦s beliefs, administrative principles, private senior high school, administrative staff