This research is a study of the heretic movement that took place during the first Abbasid era. I chose to study heresy of Bashar Ibn Burd. I tried to discover the concept of heresy in his poems. Bashar Ibn Burd was a stubborn poet who fought many battles with jurists and politicians, specially his famous battles against Wasil Ibn Ataa and the minister Yaqoub Ibn Daoud. In the third part, I tried to reveal the heresy of Bashar Ibn Burd by tracing the opinions of critics and guiding them to the heresy of Bashar. In the fourth part of the research, I tried to explore the reasons for the assassination of Bashar Ibn Burd, the research attempted to know whether this assassination took place for ideological or political reasons. Bashar tried to obtain a monetary award from the prizes -which granted by the caliph to the poets - from the Minister Jacob Ibn Daoud, but the Minister Jacob Ibn Daoud insisted that Bashar be deprived of the prizes of the caliph, so Bashar was angry, and he created a poem that satirized Minister Jacob Bin Dawood, and wrote another poem satirizing Caliph al-Mahdi. This poem was passed on to the caliph, who then ordered his death.