PM Modi is by far the most followed world leader on the gargantuan social networking platform, counting 42.7 million followers.
That is nearly twice the 24.5 million who follow Mr Trump, according to a study by communications firm Burson-Martsteller.
Of course, Facebook tends to be more widely used in Asia than Twitter which may also account for the large number of followers for Asian leaders.
Cambodia's prime minister Hun Sen shot into fifth position after his following swelled nearly 50 percent to 9.6 million people, the study found.
He therefore counts "more Facebook fans than Cambodia has Facebook users (7.1 million), but still (fewer) than the 14.4 million Khmer speakers on Facebook," it pointed out.
The study, which analysed the activity of 650 personal and institutional Facebook pages of heads of state and government and foreign ministers since January 1, 2017, meanwhile showed that Mr Trump easily counted most interactions on the platform.
It also found that Mr Trump on average posts five times a day on Facebook, which is more than double the number of posts from PM Modi.
In terms of followers, the study put Queen Rania of Jordan in third place, with 16 million followers.
Wednesday's study also highlighted the handful of world leaders who actually manage their Facebook pages themselves, instead of handing them off to social media teams.
New Zealand Prime Minister Jacinda Ardern is particularly active and is one of few who regularly broadcasts live on the platform, from her home and even from her car.
The seven-month-pregnant politician has become the "most loved" world leader on Facebook, the study found, pointing out that 14 percent of her interactions on the platform are love hearts sent by her followers.
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