"This constituent assembly is of a spurious origin and, therefore, we cannot recognize its [election] results," Santos said at a university in Barranquilla, as quoted by the presidential office.
The Colombian president added his country would continue to seek a "peaceful and hopefully prompt democratic solution" to the ongoing political crisis in Venezuela.
Venezuelan President Nicolas Maduro has called the vote for a new legislative body for this Sunday to elect 545 people’s representatives in an effort to bring peace to the country.
His decision led to nearly daily demonstrations by opposition supporters across the country that have led to more than 110 deaths since April. Many have people defied a ban on rallies and took to the streets on Friday night. At least one person died of a gunshot wound.