This is the most important and famous festivals celebrated at Palani. Lasting for a timespan of 10 days, this festival is commenced by the flag hoisting done at the Perianayaki amman temple.

On the 6th day there is a parade during which Lord Murugan gives darshan along with goddesses Valli and Deyvaanai atop the ‘Velli ther’ – Silver Car.Thousands of devotees participate in the ‘Thai Ther’ –Rathorchavam on the 7th day at the adivaram. The devotees also offer varieties of Kavadi to Lord Murugan like flowers, sugar, water, Tender coconuts, milk, and holy water…e.t.c.

On the 7th day Lord Dhandayuthapani on the hills would ride on his ‘Thanga Ther’- Golden Chariot. Thai Poosam is considered to be the festival of festivals in Palani with strength of over 3 -5lakh people visiting the temple.

The Legends associated with Thaipoosam: VEL MYTH:- This is considered to be the story behind the origination of Thai Poosam. Sages who were terrorized by the asura Tarakasuran made a plea to Lord Shiva to Destroy the Asuran. Lord Shiva sympathetic to their condition, sent his son Lord Murugan to annihilate the Asuran. Murugan, with the help of the 11 weapons provided by Lord Shiva and the powerful Vel by mother Parvathi achieved the success. It is believed that Lord Murugan killed the narakasuran during the Poosam star of the Month Thai. Hence it led to the celebration of Thai Poosam. This festival is celebrated with much fervor everywhere in Tamilnadu. People walk in groups the land to Palani with Kavadis to get the darshan of Lord Murugan during Thai poosam.

The curse imparted on Lord Murugan: Lord Shiva was providing an important mantra to Parvathi. Lord Murugan eavesdropped this. When mother Parvathi became aware of this, she cursed Lord Murugan. Lord Murugan, realizing his guilt prayed for apology. Parvathi, pleased by this, appeared with Shiva before Lord Murugan and forgive him. The day that Parvathi appeared before Murugan is celebrated as Thai Poosam.

The Cosmic dance: Another legend is that Shiva and parvathi were involved on a cosmic dance during this period, which led to the celebration of Thai Poosam.

The Kaveri legend: River Kaveri fed up with the entire attention river Ganga was receiving, prayed to Lord Vishnu. So Lord Vishnu appeared and blessed her on Thai poosam.