The complexity of science teaching requires science teachers to encounter a range of tasks. Some tasks are perceived as stressful while others are not. This study aims to investigate the extent to which different teaching situations lead to different stress levels. It also aims to identify the easiest and most difficult conditions to be regarded as stressful conditions by science teachers. An occupational stress inventory of 25 items developed by Okebukola ("1988") validation of the occupational stress inventory for science teachers. "Science Teacher," was used to measure the science teachers' stress level in science teaching. A four point Likert scale ranging from 1--"no stress at all" to 4--"extreme stress" was used. Fifty-eight Malaysian secondary science teachers participated in the survey in which six volunteered to participate in the interview study. The data was then analyzed using the Rasch model to measure the level of stress caused by different kinds of stressful conditions. Even though "overloaded science syllabus" was identified to be the basis of multiple stressful conditions, it was, however, difficult for the respondents to regard it as a stressful condition. On the other hand, the respondents found that "having to teach difficult science topics" is easiest to be regarded as a stressful condition. It was shown that even though "overloaded science syllabus" is the starting point for stress caused by multiple conditions, due to the availability of coping strategies which can be employed by the respondents, the stressor is minor in causing stress among teachers. On the other hand, when teachers lack the availability of coping strategies dealing with teaching difficult science topics, they easily feel stressful. One of the main recommendations to overcome stressful conditions is to provide the science teachers "topic specific pedagogy" during in-service training.