The launch is scheduled at 6:00 pm on December 16, at Satish Dhawan Space Centre in the spaceport of Sriharikota.
"The 59-hour countdown activity of PSLV-C29/TeLEOS-1 Mission has started at 07.00 hours today," ISRO said.
The Mission Readiness Review committee and Launch Authorisation Board have cleared the countdown, it said.
ISRO's trusted workhorse Polar Satellite Launch Vehicle on its 32nd flight would launch the six satellites into a 550-km circular orbit inclined at 15 degrees to the equator.
Of the six satellites, TeLEOS-1 is the primary satellite weighing 400kg whereas the other five satellites include two micro-satellites and three nano-satellites.
TeLEOS-1 is the first Singapore commercial earth observation satellite and would be launched into a low Earth orbit for "remote sensing" applications.
To be launched from the first launch pad, this is the 11th flight of PSLV in 'core-alone' configuration without the use of solid strap-on motors.
Antrix Corporation Ltd, the commercial arm of ISRO, has provided launch services in PSLV for 51 customer satellites from 20 countries.
Get Breaking news, live coverage, and Latest News from India and around the world on NDTV.com. Catch all the Live TV action on NDTV 24x7 and NDTV India. Like us on Facebook or follow us on Twitter and Instagram for latest news and live news updates.