More than 500 employees have left Sars this year
Replying to a parliamentary question by the DA's deputy finance spokesman, Alf Lees, Gigaba said 128 of these staff members who had departed had university degrees and 58 came from the audit division.
The average age of those who left was 43.38 years and the average length of service was 14.78 years.
Of those who left, 344 resigned, 83 retired and the services of 40 were terminated.
The reply did not provide figures for previous years, so it was not possible to determine whether the departures represented an "exodus" or were a normal pattern.
But Lees said the reply revealed "the sheer extent of the brain drain" at Sars.
"Sars has experienced institutional decay under its commissioner, Tom Moyane, and the reply confirms this. It also indicates the likelihood of continued institutional weakening," Lees said.
"Considering the critical role Sars plays in the South African economy, serious intervention cannot be delayed any further. The flight of experienced professionals from Sars means the revenue service may fail to attract critical skills and ultimately become yet another failed public entity.
"SA faces a tax revenue shortfall of R50.8bn and a further weakening of key institutions like Sars could possibly worsen the situation, leaving the 9.4-million unemployed South Africans with little hope under the failing ANC government," he said.