Doctors involved in the treatment of the 75-year-old Nepali Congress leader have given a clean bill of health to him and said he was recuperating well.
"The doctors have said that he no longer has symptoms of cancer, which is a good news for us," said Nepali Congress leader Laxman Ghimire.
Koirala had undergone a successful radiotherapy treatment for lung cancer at New York's Sloan Kettering Cancer Centre three months ago.
Nepal Prime Minister is in new York to participate in the UN General Assembly session.
After conducting scans the doctors have found that Koirala's lungs are now free of spots and lesions detected three months ago, he said.
Koirala, was a regular cigarette smoker until he was diagnosed with tongue cancer eight years ago and he has been visiting the New York-based hospital for annual follow-ups after undergoing surgery.
He became Prime Minister in February with the support of CPN-UML after Nepali Congress emerged as the largest party in the second Constituent Assembly elections held in November last year.
The government has pledged to promulgate a new constitution within a year.
Koirala's health has concerns for Nepalese people who are waiting for the new constitution to be promulgated.
