Annonacin is an environmental neurotoxin identified in the pulp of several fruits of the Annonaceae family (for example in Annona muricata, Asimina triloba), whose consumption was linked with the occurrence of sporadic atypical Parkinsonism with dementia. Pharmacokinetic parameters of this molecule are unknown. A method for its quantification in Rat plasma was developed, using its analogue annonacinone as an internal standard. Extraction from plasma was performed using ethylacetate with a good recovery. Quantification was performed by UPLC–MS/MS in SRM mode, based on the loss of the γ-methyl-γ-lactone (−112 amu) from the sodium-cationized species [M + Na]+ of both annonacin and internal standard. The limit of quantification was 0.25 ng/mL. Despite strong matrix effects, a good linearity was obtained over two distinct ranges 0.25–10 ng/mL and 10–100 ng/mL. The intra- and inter-day precisions (RSD) were lower than 10%, while accuracy was within ±10%. This method was applied to a pharmacokinetic study in the Rat. After oral administration of 10 mg/kg annonacin, a Cmax of 7.9 ± 1.5 ng/mL was reached at Tmax 0.25 h; T1/2 was 4.8±0.7 h and apparent distribution volume was 387.9 ± 64.6 L. The bioavailability of annonacin was estimated to be 3.2 ± 0.3% of the ingested dose.