To quantify Ribociclib in plasma samples employing Gefitinib as an internal standard (IS), a straightforward, efficient, and selective LC-MS/MS approach was designed. Using an Agilent, Zorbax, XDB C18 (2.1 x 50 mm ID, 5 μm) column, the process of separating was carried out on an isocratic mobile phase entailing acetonitrile (ACN) and 0.1% formic acid in water (70:30) at 0.120 mL/min. In the context of MRM positive mode, ribociclib and Gefitinib were discovered to have parent ions at m/z 435.60 and 447.10, correspondingly, while the daughter masses were determined to be 322.10 and 127.90, correspondingly. The medication and IS were extracted via the protein precipitation (PP) technique. The correlation value (r2) was 0.99934, validating the approach throughout linear concentration levels of 1.0-1000.0 ng/mL. The accuracy spanned between 96.00 - 102.08 and the precision spanned between 0.008 - 8.5%, according to this strategy. Benchtop, postoperative, and long-term stability investigations all revealed that ribociclib was stable.