Police found items of military memorabilia, much of it decommissioned, during a search yesterday morning of a farm in Toftshaw Lane, Bradford, when they responded to a report of a domestic assault.
The grenades were destroyed in a nearby field in a series of controlled explosions.
Some nearby properties were evacuated during the operation.
Bradford South acting Superintendent Mark McManus said: “The initial searches uncovered a number of decommissioned military memorabilia, however two live grenades were also located and a controlled explosion took place to make these safe.
“There is no immediate threat to residents and we will be continuing our searches into the evening to ensure no further devices are on the site.
“A 36-year-old man remains in custody and will be interviewed by officers in relation to the finds.”
Police were called to the scene at 5.30am yesterday.
A 62-year-old man was found with minor facial injuries.
The arrested man was arrested on suspicion of assault.
A West Yorkshire Police spokesman said the area had been evacuated as a precaution while firearms experts were contacted.
Officers from the neighbourhood policing team spent time yesterday patrolling the area to offer reassurance and to respond to any concerns from local residents, said the spokesman.