Klajn published a book "Kako se gaje uljane biljke" (How are grown oilseed plants) in 1938.

In Osijek Klajn was named secretary of the provincial committee of the KPJ for eastern Slavonia.

His work as a communist and a Jew was noticed by the regime of a newly founded Independent State of Croatia.

Klajn withstand the torture and never provide the required information about the KPJ organizations and membership.

In 1959 bust of Mihajlo Klajn was revealed at the Faculty of Agriculture, University of Zagreb as an honor to his sacrifice.