The fifth election to South Glamorgan County Council was held in May 1989. It was preceded by the 1985 election and followed by the 1993 election.
There were no boundary changes at this election.
Conservative and Labour candidates contested all seats. Following the break-up of the SDP-Liberal Alliance, most seats were contested by both the Social and Liberal Democrats and the continuing SDP. There were a smaller number of Plaid Cymru and Green Party candidates and a few Independents.
Labour retained control with an increased majority, by capturing a number of Conservative seats. A few other seats also changed hands. The Social and Liberal Democrats held all their seats bar one, but polled poorly elsewhere.
A by-election was held on the same day in the Vale of Glamorgan constituency. This resulted in a much higher turnout than usual for local elections in wards which lay within the constituency. Labour captured the parliamentary seat from the Conservatives.
This table summarises the result of the elections in all wards. 62 councillors were elected.
One of the Labour 'gains' was in Thornhill ward which the party had already won at a by-election.
The seat had been won by an Alliance (SDP) candidate in 1985 but was gained by Labour at a subsequent by-election.
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<nowiki>*</nowiki> <small>existing councillor, for the same ward</small>
Two by-elections were held on 2 May 1991, the same day as elections to Cardiff City Council. Both were defended by the Liberal Democrats with one of the seats being narrowly lost to Labour.