Siponimod is novel alkoxyimino derivative indicated for the treatment of adult patients with secondary progressive multiple sclerosis. LC-MS/MS method developed for the estimation of siponimod in rat plasma using fingolimod as internal standard (IS) with wide range of linearity from 0.050 to 1000 ng/mL. Protein precipitation technique was used to extract both siponimod and fingolimod by adding 200 µL of acetonitrile to 100 µL plasma. 0.1% formic acid in Milli-Q water used as mobile phase-A and 0.1% formic acid in acetonitrile used as mobile phase-B in gradient mode to achieve good baseline. Kinetex C18 column used to achieve the separation with in short chromatographic run of 1.50 minutes. Positive electrospray ionization mode used to quantify the both siponimod and internal standard in multiple reaction monitoring (MRM) mode. The developed method is rapid and selective for estimation of siponimod with good sensitivity at lower limit of quantification of 0.050 ng/mL. The standard curve is linear in the range of 0.050 to 1000 ng/mL, with r2> 0.9997. The intra- and inter-day precision and accuracy results met acceptance criteria as per Food and Drug Administration (FDA) guidelines. Bench top, auto sampler, long-term storage and freeze thaw cycle stability established to know the stability of analyte and IS. The developed method was fully validated and can be applied to pharmacokinetic studies.