Acorn Park Care Home in East Kilbride, South Lanarkshire, was warned it must make a "significant improvement".
If not, it could face having its registration cancelled.
The privately-run home was served with a formal improvement notice by the Care Inspectorate and given until next month to make changes.
Seven areas of concern were listed after an inspection, with nutrition and hydration, personal plans for service users, environmental safety, staffing and administration of drugs all being criticised.
A spokesman for the Care Inspectorate said: "Everyone in Scotland has the right to safe, compassionate care which meets their needs and respects their rights.
"Where we have concerns, we do not hesitate to take action.
"Our first priority is always the safety and well-being of residents and this improvement notice sets out what we expect the service to do to ensure that the care provided to residents improves.
"We will be inspecting this service again soon to ensure that progress is being made."
An Acorn Park spokesman said: "We are working hard with the Care Inspectorate to meet their requirements within the timescales set."

The loggerhead turtle was affected by the cold, had shell damage and had signs of an infection.
It was found on the stretch of beach between the Dicq shack and Rice bowl and was taken to the nearby New Era Veterinary Hospital for treatment.
After an appeal it is being moved to a special tank at the fresh fish company at La Collette.
A number of turtles have washed up in the UK in recent months, but most have been too ill to save.
Vets have been treating it with antibiotics and fluids and say the turtle has a "poor prognosis".
They will use the tank to slowly raise its temperature.

Led by "generals" Mohammed Sajjad, 38, from Cardiff, and Imtiaz Ali, 35, from Newport, the group were involved in bringing the class A drug into Wales.
Cardiff Crown Court heard the group was arrested as part of one of the largest undercover operations in Wales.
Four were convicted after trial, while six others pleaded guilty to their part in the conspiracy from 2013-2014.
Arrests were made after police seized 40kg (88lbs) of the drug in 2014.
Most was found inside a speaker and a suitcase in a car stopped on the M5, while a smaller amount was discovered in the footwell of a taxi in Newport.
Officers said the seizure had prevented half a million drug deals, the court heard.
Sentencing the group, Judge Stephen Hopkins QC, said the gang had dealt in "industrial quantities" of the "highly addictive evil drug".
There have been more heroin seizures across the South Wales Police force area than anywhere else in Wales and England, outside London, for at least the past three years, according to figures from the Home Office.
During 2014-2015, South Wales Police made 303 heroin seizures per million people. The average for Wales and England was 135 seizures per million.
A force spokesman said: "There is a greater focus from the Regional Organised Crime Unit (ROCU) utilising the control strategy - which enables us to prioritise a coordinated approach on regional crime groups and the traffic of drugs."
A care home has been ordered to raise its standards after the industry watchdog criticised areas including infection control.
[NEXT_CONCEPT]
A turtle which was found on a beach in St Clement is being treated at a veterinary hospital in Jersey.
[NEXT_CONCEPT]
Ten members of a gang who conspired to supply £5m worth of heroin have been jailed.