In oil well cementing, cement must flow through the casing before reaching the targeted annulus; hence, a retarder must be added to provide the cement with sufficient time to reach the targeted depth before setting. At the same time, in support of the Paris Agreement, the prospect of substituting ordinary Portland cement (OPC) with geopolymer cement as the well cement material has to be further explored. Although previous studies have found that retarders can delay the strength development of the cement, the studies were conducted either under ambient conditions or using OPC; hence, the findings do not apply to geopolymer cement that is exposed to wellbore conditions. In order to address the shortcomings of the studies, an addition of a hydroxycarboxylic acid-based retarder to a fly ash-based geopolymer cement, at concentrations of up to 3 by weight of the fly ash, was performed. The slurry of the cement was aged at 100� C and 20.7 MPa for 8, 24 and 48 h. Compressive strength tests were conducted on samples of the cement. At the 8 h aging duration, retarder concentrations of 0.5�2.0 led to strength increases of 112.7�129.4 relative to that of 0, or the control sample, whereas that of 3.0 led to a strength decrease of 84.2. At the 24 h aging duration, all retarder concentrations led to strength decreases of 16.4�22.5. At the 48 h aging duration, retarder concentrations of 1.0�3.0 led to strength increases of 18.1�24.4, whereas that of 0.5 led to a strength decrease of 16.7. © 2023 by the authors. Licensee MDPI, Basel, Switzerland.