The NHS Trust says it's because the new variant of Covid-19 has caused a surge in cases in the community.
Oxford Health says the decision to restrict visiting during lockdown 'has not been taken lightly'.
Visits will only be allowed under exceptional circumstances, like when a patient is at the end of their life.
The Trust added that it 'recognised that this will have an impact on our patients and their loved ones.'
Oxford Health runs a number of sites like the Abingdon, Bicester and Witney Community Hospitals, and the Littlemore Mental Health Centre.
You can see a full list here.
Community services Clinical Director Pete McGrane said: ‘As the situation in the community deteriorates and with the new variant of Covid thought to be behind the surge in positive cases, we have a duty of care to protect our patients, our staff and the public, keeping everyone as safe as possible during this critical time.’
Visits will only be permitted under exceptional circumstances and extreme caution will need to be taken, according to the Trust.
On mental health wards for example, face-to-face visiting will not be permitted 'unless it would have a detrimental impact on their wellbeing.'
A full risk assessment would be needed though to reduce likely transmission risks to patients and staff, whilst distancing, hand sanitising and face mask rules would need to be followed.
Instead of visiting Oxford Health's community hospitals and mental health units, families are being encouraged to use the 'Letters to a Loved One' service where messages can be emailed to firstname.lastname@example.org and delivered to the bedside of the patient.
Every bed is also allocated an iPad or tablet for video calls and messaging, which staff are on hand to help with.