The friends, Mohamad Aidilfitri Mohd Powet and Mohd Afiq Jamli, both aged 21, made the guilty plea after the charge was read out to them before judge Slamat Yahya.
They were alleged to have assaulted the 37-year-old woman, bound her legs and then placed her in a gunny sack before throwing her into the Sungai Klang with the intention of killing her.
The victim, who is a factory worker, was rescued by passers-by.
The two men, both unemployed, were alleged to have committed the offence at the Sungai Klang bridge, Kemuning-Shah Alam Expressway (LKSA), Section 24 here, about 11am last Feb 6.
They were charged under Section 307 of the Penal Code and face imprisonment for up to 20 years if found guilty.
Slamat set March 15 for sentencing, following a request by the prosecution, conducted by deputy public prosecutor Naliatul Huzaimi Ab Rasip, pending the probation report on the accused from the Social Welfare Department.
The two accused were denied bail.