Background/Aim: Success of tooth replantation depends on the quality and quantity of periodontal ligament (PDL) cells. The aims of this study were to evaluate Thai propolis extract as a storage medium for maintaining PDL cell viability and preserving gene expressions in PDL tissues. Materials and Methods: PDL cells from human premolars were tested for cytotoxicity of the extract by PrestoBlue assay to determine a non-toxic concentration. Subsequently, 96 freshly extracted premolars were allocated into different treatment groups. Control groups were freshly extracted premolars or they had been stored dry for 12 hours. Experimental avulsed teeth were created by leaving them air-dried for 30 minutes immediately after extraction, then they were immersed in Thai propolis extract, HBSS or milk for 3, 6 and 12 hours. After tooth storage, the remaining PDL cells were determined for their cell viability. RNA isolated from PDL tissues of three premolars treated similarly was analysed for periostin and S100A4 expressions using RT-qPCR. Results: Thai propolis extract at 0.625 mg mL −1 promoted the greatest PDL cell viability. Tooth storage in 0.625 mg mL −1 Thai propolis extract, HBSS or milk showed no difference in maintaining cell viability. Periostin mRNA level was preserved by Thai propolis extract. Expression of S100A4 mRNA in PDL tissues stored in all tested media was dampened. Conclusions: PDL cells from mock avulsed teeth stored in 0.625 mg mL −1 Thai propolis extract for 3, 6 and 12 hours remained viable and the expression of periostin was preserved. This study suggests this extract as an alternative for a tooth storage medium for up to 12 hours. However, transporting an avulsed tooth in a storage medium for extended extra-oral time might affect the PDL cell phenotypes.