The majority of Czechoslovak jews were murdered by the National Socialists in the Holocaust. Those who survived either emigrated to the United States (this was mostly the case for the Orthodox) or completely abandoned their jewish identity (in many cases they would not even tell their children about their ancestry).

After the communist takeover in February of 1948, the situation of these Czechicised "jews" was not any different than of the majority population. In fact a significant number of Czechoslovak communists had jewish ancestry. The change in the party line came after Israel aligned itself with the West in the Cold war. Stalin started an anti-semitic campaign in the USSR, known as the case of the saboteur-doctors and demanded that his satelite states conduct similar purges of "zionist" communists. In Czechoslovakia, these event are known as the Slánský trials of 1952. Fourteen leading communists with a jewish background (including Rudolf Slánský - the general secretary and second most powerful man in the party) were arrested, accused of being zionist and nationalist conspirators, tortured to make a confession, and put on trial. Their guilt was already decided beforehand by the Party, the trial was only a staged show for the public (the entire process was scripted and the accused had to memorise their confession and recite it in front of the court). Eleven of the fourteen (inluding Slánský) were sentenced to death, the other 3 got a life sentence.

Even after the party decided to formally denounce "the errors of Stalinism" in 1960, people with jewish ancestry were stil regarded as problematic and potentially dangerous for the regime. In 1971 the STB (the secret police of Czechoslovakia) started "Operation Spider". It was a network of spies and informers that were closely monitoring the lives of 20 000 jewish Czechs and Slovaks that were still living in the country. Needless to say, this operation included the harassment and abuse of individuals (and their family) who for various reasons did not conform to the ruling marxist ideology, for example by showing any interest in Judaism. Among the victims of operation spider was the current Chief Rabbi of Czechia - Karol Sidon, who converted to Judaism in 1978, and, after years of harassment by the secret police, was forced to leave Czechoslovakia in 1983.