After the outbreak of the Spanish Civil War, he volunteered to fight in the International Brigades. He served as a political commisaire in the 129th International Brigade, battalion Masaryk, between 1937–1939. He fought at the fronts in Extramadura, Aragon, Levante and as the rear-guard during the retreat from Catalonia to France. After crossing the Pyrénées, he was interned in French internment camps in St. Cyprien and Gurs. In both camps he was the head of illegal organization of Czechoslovak communists. In October 1939 he was transported together with other „Komintern agents“ to the concentration camp Vernet.