A Care Inspectorate report has found that some staff at Kingsmead in Kingswells were not treating people with "dignity and respect".
Some residents had lost weight, with concerns being raised that their nutritional needs were not being met.
The report said that in some incidences, people were being treated like "objects".
The report said one lunchtime service was "chaotic" and the dining experience for people was "very poor".
It said management and staff displayed poor knowledge of clinical needs.
The report called for significant improvements, including staff development.
Mike Best, group managing director of Mead Medical Holdings, said they were concentrating on reducing the number of agency staff, increasing the number of permanent staff and looking at raising standards in the way they operated.
The home can provide care for up to 55 older people, and up to 10 adults with learning disabilities.

Thousands of people were at the ceremony at BAE Systems' Devonshire Dock Hall in Barrow to mark the end of the build process for Artful.
Another four of the nuclear-powered submarines are being built at the yard.
The ceremony was carried out by Amanda Lady Zambellas, wife of the Royal Navy's First Sea Lord, Admiral Sir George Zambellas.
BAE Systems Maritime - Submarines managing director John Hudson said: "The design and build of a nuclear-powered submarine is as challenging as it is complex, so today represents a significant milestone in Artful's programme.
"It requires real skill and innovation to deliver submarines as sophisticated as Artful and this would not have been possible without the valued contribution of our employees and the collaborative efforts of the whole submarine enterprise."
Artful will remain at the Barrow yard while commissioning activities are carried out and is due to be launched early next year for further tests.
HMS Astute and HMS Ambush have already been launched. The other vessels are at various stages in the design and build process and will be called Audacious, Anson, Agamemnon and Ajax.
The Barrow yard has been working on the Astute programme since 2001.
The Ministry of Defence said the Astute class of submarines have greater firepower, state-of-the-art communications equipment and advanced stealth technology, making them quiet and harder to detect.

The Japanese firm expects net profit in the year to March of 1.7 trillion yen ($15.1bn; Â£12.1bn), compared with a previous forecast of 1.55 trillion yen.
That is despite losing its top-selling carmaker status to Volkswagen in 2016,
Meanwhile, Toyota said it had begun formal talks to work with Suzuki on projects including safety technology.
Analysts said the partnership - which could also involve collaboration on vehicles that were less damaging to the environment - would give Suzuki access to Toyota's technology. Benefits for Toyota are likely to include tapping in to Suzuki's strong market position in India.
The forecast for 2016-17 profits is still below the 2.1 trillion yen profit it recorded a year earlier.
But with Japan's yen weakening against the dollar, it will benefit from sales overseas which are worth more when converted back into the local currency.
Like other Japanese carmakers, Toyota is watching closely for any trade tariffs introduced by the new US administration.
At the moment, only about half of the cars it sells in the country are manufactured locally. Last month, US President Donald Trump criticised it for making vehicles in Mexico to sell over the border.
The US is its biggest market, and it is struggling to meet demand for bigger vehicles such as sport utility vehicles. Lower petrol prices have made such models more affordable to drive.
The quality of care at an Aberdeen nursing home has been deemed "unsatisfactory".
[NEXT_CONCEPT]
The third Astute Class submarine to be built at a Cumbrian shipyard has been named.
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Toyota says its full-year profits will be better than expected thanks to a pick-up in sales and a boost from currency fluctuations.