Telkom chief executive Papi Molotsane has quit after 18 months in the job, the company said on Thursday.
The fixed-line telecommunication giant gave no reason for his resignation.
It said Reuben September will take over as acting CEO, and that it will start looking for a permanent replacement.
Molotsane has reportedly been the target of criticism from shareholders over his leadership of the company.
Telkom chief technical officer, Thami Msimango, resigned in March, as did chief sales and marketing officer Wallace Beelders. Both said they wanted to pursue other career opportunities.
Telkom spokespersons were not available for further comment when contacted by the Mail & Guardian Online on Thursday evening.