Ronald Maddison thought the aim of the tests was to find a cold cure
No scientists will be charged over a series of chemical tests on human volunteers at the Ministry of Defence's laboratories at Porton Down.
Between 1939 and 1989, hundreds of servicemen took part in experiments at the Wiltshire establishment.
The Crown Prosecution Service (CPS) carried out a review after an inquest ruled a County Durham aircraftsman who died in 1953 was unlawfully killed.
But the CPS has decided there is insufficient evidence to prosecute.
Leading Aircraftsman Ronald Maddison's family say he went to Porton Down believing he would be taking part in tests to find a cure for the common cold.
Instead, Mr Maddison, from Consett, was exposed to the lethal nerve agent sarin, and died within an hour.
The initial inquest into his death was held in secret on the grounds of national security, but after years of campaigning a second inquest was opened in 2004. It decided LAC Maddison had been unlawfully killed.
Last month it was revealed his family had been awarded £100,000 in compensation from the Ministry of Defence
Kate Leonard, Senior Crown Prosecutor, said: "I have decided there is still insufficient evidence available to prosecute any person with a criminal offence over the testing which was carried out.
"In reaching these decisions I considered the evidence from the inquest into Mr Maddison's death to see whether it had any impact."