Age UK said loneliness was a "huge issue" in Britain after a poll found one in 10 people over the age of 65 often or always feel lonely.
One in eight said they felt cut off from society and 30% said they would like to go out more often.
Of 2000 pensioners surveyed, 37% said their TV was their main form of company.
The charity is calling on members of the public to send donations so it can reach more lonely older people through its services.
It warned extreme loneliness can increase the chance of an early death.
Age UK's charity director Caroline Abrahams said: "Loneliness not only makes life miserable for older people, it is also really bad for their health making them more vulnerable to illness and disease.
"It is time to take loneliness seriously and that's why we're asking everyone to take action by donating today to help us carry on supporting older people."