Religious fundamentalism phenomenon is complex social concept that demands interdisciplinary access. Psychological and theological assumptions must be considered in order to get correct understanding. Although going different ways, psychology and theology often come to the same conclusion. People’s nature’s complexity demands careful approach. Behind generally known problems of aggressiveness, truthfulness and kindness, new views can be found. They throw new light on religious fundamentalism. In that way, we come to a better understanding and possible suggestions from psychological and theological standpoint. They could give their contribution in prevention of this phenomenon which is often simplified in public.