The change of the ownership share in Sky Towers Infrastructure has been registered in the business entities register, Telekom Srpske said in a bourse filing.
The name of the buyer was not disclosed.
Telekom Srpske said in May it has established the Banja Luka-based company for wireless telecommunications, without providing further details.
Telekom Srpske, majority-owned by Telekom Srbija, has clients mainly in the Serb Republic entity, which forms Bosnia and Herzegovina together with the Federation entity.
Telekom Srpske's shares closed flat at 1.19 marka ($0.65/0.61 euro) on the Banja Luka Stock Exchange (BLSE) on Monday.
Bosnia, a country of some 3.5 million people, has two more major telecommunication companies, both state-controlled - HT Mostar and BH Telecom.
(1 euro = 1.95583 marka)