Kolli Hills or Kolli Malai is a small mountain range located in Western Tamil Nadu and spreaded over the Namakkal district of India. The mountains rise to 1300m in height and cover an area of approximately 280 km². They are part of the Eastern Ghats, which is a mountain range that runs mostly parallel to the east coast of South India. The mountain is a site of pilgrimage, because of the Arapaleeswarar temple, but the area is also popular with Motor cycle enthusiasts because of the high altitude motor-able terrain with 70 hairpin bends.

The Kolli hills became taluk and forms a part of Namakkal district. Semmedu village is the headquarters for the Kolli hills and Semmedu is connected by road to Namakkal and Salem. Nowadays the Bus service is provided up to Arappaleeswarar Temple. BSNL (earlier DOT) established the first Telecommunication networks (LDPCO) in 1977 and afterwards the Telecom facilities are continuously expanded depending upon the requirements at Kolli hills.

Kolli Hills is visited by nature lovers, hikers, trekking clubs, tourists and meditation practitioners among hill stations in Tamil Nadu. Agaya Gangai is the waterfall situated near the Arappaleeswarar temple.