Once the match was reduced to nine overs a side, the hosts defended their total of 64 with Marizanne Kapp and Ayabonga Khaka picking up five wickets
The 32-run win in Bloemfontein put the hosts one victory shy of another clean-sweep, having claimed the ODI series 5-0.
Rumana Ahmed and Fargana Hoque add 72 to keep Bangladesh in the hunt before Shabnim Ismail knocks them over to close out the game
For the fifth time in as many matches, South Africa cantered to victory with the help of several performances all through their line-up
The visitors went 0-4 down, even as Lizelle Lee became only the third South African woman to cross the 2000-run mark in ODIs
Bangladesh women bowled out for their second sub-100 score as they go 3-0 down in the five-match series
South Africa secured victory with nine wickets and 32.5 overs to spare to go 2-0 up in the five-match series