"Friday's deadline will not be extended. Taxpayers who fail to meet this deadline will face administrative penalties that accumulate monthly for every month that a return is outstanding," Sars said in a statement.
The deadline applied to non-provisional taxpayers - or those whose source of income was a monthly salary.
So far, about 3.2 million returns were submitted to Sars since the start of Tax Season 2010 on July 1.
"Of this total more than 1.7 million returns have been submitted electronically via eFiling while Sars branch offices have assisted more than 1.3 million taxpayers to submit their returns electronically to date," Sars said.
Provisional taxpayers - people who have additional sources of income such as taxable interest - had until January 31, 2011 to submit their tax returns.
By the end of last week, Sars had received about 100 000 more returns than the corresponding period last year.
"For Sars this is a very encouraging trend in that more taxpayers are submitting tax returns early to avoid the last minute rush to Sars offices which has been a regular feature in the pattern of filing during previous years."
Sars will extend its services in various venues across the country this week to assist last-minute taxpayers.