The children's ward in Ealing Hospital is set to close today (June 30).
Campaigners, led by Ealing Save Our NHS, will protest outside the hospital in Southall from 12.30pm.
The closure was confirmed on May 18 at a heated Ealing Clinical Commissioning Group (CCG) meeting.
The ward 16 beds, including four day assessment beds, and cares for 10 to 12 children at any one time for those requiring emergency treatment or an overnight stay in hospital.
Under changes by SaHF, launched by a series of CCG's in 2012, ambulances will no longer take children to the A & E unit at the Uxbridge Road hospital.
The children's ward is also referred to as the Charlie Chaplin ward.
SaHF have faced intense criticism for their reforms, with an Independent Healthcare Commission report, led by Michael Mansfield QC, calling for an "immediate halt" .
And in April, MPs in west London wrote to the government to demand an investigation.