Mieczysław Jastrun born as Mojsze Agatstein (29 October 1903 – 22 February 1983) was a Polish poet and essayist of Jewish origin. The main themes of his poetry are: philosophy and morality. He translated French, Russian and German poetry to Polish.

Born in Korolówka (in the former Eastern Galicia) in a Jewish family, the son of Józef Agatstein and Maria Agatstein née Wiensohn. He spent his childhood in Jodłowa, he went to public school in Ryglice, where his father had opened a surgery. The family moved several times to places where Joseph worked. Through 1915−1919 Mieczysław w Cracow, where he went to gymnasium. Due to the onset of Polish–Soviet War he interrupted his studies and volunteered to the Polish Army. However, he did not participate in engagements as he contracted typhus. On 9 March 1920 together with his older brother, Jerzy Stanisław (later Jerzy Gierowski) he was baptised in the parish church in Jodłowa. He did not return to Cracow and he completed the last two high school forms in First General Liceum in Tarnów. During that time he lived in Pleśna, with his former governess (1921−1923).