Epoxy or oxirane compounds have attracted considerable interest and commercial importance in recent years. The study on the synthesis of trimethylolpropane (TMP) ester is well established. However, the study on the epoxidation of the oleyl-based TMP is still limited. Therefore, the present research concerns the characterisation of epoxidised TMP trioleate which could be used as plasticiser, high stability biolubricants and feedstock for the subsequent reaction such as acrylation to produce bio-based polymer and resin. The effect of the molar ratio of ethylenic unsaturation in TMP trioleate to formic acid for in situ peroxidation has been investigated. The resultant epoxidised TMP trioleate containing different numbers of epoxide groups/molecule were synthesised. The high ratio of formic acid to ethylenic unsaturation in TMP trioleate is unfavourable for in situ epoxidation as it yielded lower amount of epoxy ester. The epoxidised TMP tritrioleate was synthesised, confirmed by Fourier transform infrared (FTIR) and the degree of epoxidation (DOE) was quantified by nuclear magnetic resonance (NMR). The epoxidised TMP trioleate which contained TMP 9, 10-epoxystearic acid and TMP 9, 10, 12, 13-diepoxystearic acid were also identified. The thermal stability were compared and it was found that the epoxidised TMP trioleate has lower thermal degradation temperature than TMP trioleate.