Both men, who are the only players still playing in the PSL to have scored over 100 goals, have signed one-year deals after their contracts expired at the end of June.
After having a good season last term, Usuthu have decided to keep both players.
Nomvethe, who has played for Soweto giants Orlando Pirates and Kaizer Chiefs, netted twice in the past season to take his tally in the PSL to 121 goals.
Khenyeza, also a former Chiefs player, netted four times last season to take his tally to 110 in the PSL.
Speaking at the club launch for the new kit for this coming season in Phoenix at Spar's depot in Durban, AmaZulu general manager Lunga Sokhela said both players have been retained for the coming campaign.
''We have finalised their contracts for another year,'' Sokhela told the media.
The club also officially unveiled Argentine striker Emiliano Tade, Nhlanhla Vilakazi, Moeneeb Josephs, Marc van Heerden, Pirates graduate Charlie Hlalele, ex-Uthongathi FC defender Xolani Silawula and former Platinum Stars defender Boiki Modikaseng.