The Anne Rowling Regenerative Neurology Clinic at the University of Edinburgh was established with a 10 million pounds donation from the author in 2010, the BBC reported.
Her latest donation will help create new facilities and support research.
Anne Rowling died aged 45 from complications related to MS.
The centre is an integrated care and research facility focusing on MS and neurological conditions with the aim of bringing more clinical studies and trials to patients.
"When the Anne Rowling Clinic was first founded, none of us could have predicted the incredible progress that would be made in the field of regenerative neurology, with the clinic leading the charge," JK Rowling said in a statement on Wednesday.
"It's a matter of great pride for me that the clinic has combined these lofty ambitions with practical, on the ground support and care for people with MS, regardless of stage and type; I've heard at first-hand what a difference this support can make.
"I am confident that the combination of clinical research and practical support delivered by Professor Siddharthan Chandran and his exemplary team will create a definitive step-change for people with MS and associated conditions."
Chandran, director of the clinic, said: "Our research is shaped by listening to, and involving, individuals who are living with these tough conditions."
( With inputs from IANS )