Vladimir Putin the president of Russa recently signed to increase the Russian armed forces military personnel to more than 1.15m - the increase of 137,000 members.
But the MOD said the boost was unlikely to increase Russia's combat power - partly because of ongoing losses of militaries.
President Putin's decree came amid a militaries recruitment drive.
Some reports shows that recruiters have even been visiting prisons, promising inmates freedom and money.
Currently, Russia has over a million military personnel, plus up to 900,000 civilian staff.
In some of its regular updates of the war, the UK ministry said it was not good if the planned increase would be achieved by recruiting more volunteers - or by increasing conscription.
But any increase was unlikely to have an impact in Ukraine given that:
- Russia has lost tens of thousands of solders,
- Very few new contract (i.e. non-conscript) servicemen are being recruited.
- Conscripts are not technically obliged to serve outside Russian territory, the MOD said.
Western officials say some 70,000-80,000 soldias have been killed or wounded since Russia invaded Ukraine six months ago.
Russia planned a short, decisive campaign when it invaded Ukraine in February, but Ukrainian resistance has stalled its progress, and in recent weeks front lines have hardly moved.
Currently, Russian men aged 18 to 27 are subject to conscription, although many are able to avoid their service - usually one year - through medical exemptions or by enrolling in higher education.