The actor, who played Mr. Spock in the sci-fi TV series, was taken to UCLA Medical Center in LA earlier this week suffering from chest pains.
Nimoy had recently revealed he was fighting a serious lung disease and had been in out of hospital multiple times over the last few months.
After quitting smoking 30 years ago, the actor revealed his diagnosis on Twitter and urged smokers to kick the habit.
“I quit smoking 30 years ago. Not soon enough. I have COPD. Grandpa says, quit now!! LLAP [Live Long And Prosper]’
COPD (Chronic Obstructive Pulmonary Disease), obstructs sufferers’ breathing as their airways narrow.
I quit smoking 30 yrs ago. Not soon enough. I have COPD. Grandpa says, quit now!! LLAP— Leonard Nimoy (@TheRealNimoy) January 30, 2014
Don't smoke. I did. Wish I never had. LLAP— Leonard Nimoy (@TheRealNimoy) January 11, 2015
Symptoms of the disease, which is often caused by smoking and gets worse over time, include breathlessness, persistent coughing and frequent chest infections.
The star was recently spotted in a wheelchair and using an oxygen cylinder at JFK airport in New York.
Leonard, who officially retired in 2010 after abdominal surgery, had made a number of TV and film comebacks including a successful run playing Dr. William Bell on the hit science fiction thriller ‘Fringe’ until 2012.
Earlier this month he revealed he planned to share personal poetry from his book These Words Are For You with his 1.1m followers.
"A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP," he tweeted just five days before his death.
A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP— Leonard Nimoy (@TheRealNimoy) February 23, 2015