This ended a four-month contraction after the resolution of a protracted strike among metals and engineering workers.
Demand improved in the month while output stabilised and new orders expanded slightly, but new export orders contracted, pointing to continued pressure on the economy, HSBC said on Wednesday.
Africa's most advanced economy narrowly avoided falling into recession in the second quarter but will likely register anaemic growth this year after wage strikes hit platinum output as well as the metals and engineering industries.
"While the end of strike activity in key sectors should support stronger economic activity in the months ahead, the inflationary impact of high wage settlements was also evident in the PMI readings," HSBC economist David Faulkner said.
Staff costs increased at their fastest pace in almost two years, putting upward pressure on overall input prices, the August survey showed.