"I extend my full support to our honourable Prime Minister Narendra Modiji's Swachhata Hi Seva mission. Cleanliness is godliness," Rajinikanth tweeted.
Earlier this week, Modi had written personal letters to celebrities, industrialists and noted personalities to enlist their support for the initiative.
Quoting Mahatma Gandhi, Modi said Swachhata is for each of us to practice.
He also said the days leading up to Gandhi Jayanti on October 2 be about "encouraging widespread participation in cleanliness initiatives across the country."
In response to Modi's letter, Rajamouli tweeted: "Modi ji, heartfelt appreciation for this wonderful initiation. I'll do my best to be a part of my Swachh Bharat."