Antun Branko Šimić is counted among the most distinguished representatives of Croatian literary expressionism. He worked in line with the spirit of European expressionism, yet his work is considered exceptionally original. He advocated for art to be free from any aesthetic conventions, reflecting subjective reality and evoking emotions. Šimić was revolutionary in introducing free verse into Croatian literature. This thesis will examine his lyrical opus imbued with Eros and Thanatos, which find their origins in psychoanalytic theory and represent some of the fundamental motifs of Šimić's work. In the corpus dealing with themes of Eros, poems such as Mrtva ljubav, Tužaljka, Kada sam s tobom, životinja sav sam... will be analyzed, highlighting themes of romantic downfall, cosmic and erotic love. In the corpus with themes of Thanatos poems such as Mrtvo bit će sve..., Ukop druga, Tijelo i mi will be analyzed, reflecting a resigned approach to death, the experience of another's death and reflection on one's own mortality. Through shaping his poetic world, Šimić expressed his own states of mind and perceptions of love and death, which are rooted in both life circumstances and religious beliefs.