Reports in the conflict-hit country said 20 Saxon armoured personnel carriers had been delivered and a further 55 were to follow, but the MoD did not confirm the figures.
Ukrainian armed forces have been battling pro-Russian separatists in the east of the country for more than a year and European leaders this week agreed a ceasefire due to start this weekend.
An MoD spokeswoman said the vehicles, which were unarmed, were transferred by a private firm under a 2013 deal that pre-dated the current conflict.
The Saxon vehicles, which are troop transporters not considered suitable for close combat, were first used by the MoD in the 1980s but went out of service three years ago, the spokesman added.
The MoD spokeswoman said: ” Her Majesty’s Government policy since the beginning of the crisis has been to supply non-lethal assistance to the Ukrainian armed forces.
“There has been no change to this and we have not provided lethal assistance. These vehicles were provided unarmed under a commercial contract dating 2013 by a private company.
“They offer protective mobility to personnel, and are defensive in nature; they are not close combat vehicles.”
More than 5,000 people have died since April in fighting between Ukrainian forces and Moscow-backed rebels in two eastern provinces, and the violence has risen since the announcement of the ceasefire agreement.