Inhibitor which is a novel ovarian cancer drug. For applicability to pharmacokinetic study, a LC-MS/MS based method for monitoring plasma levels of niraparib was developed. The analyte and Olaparib(IS) were chromatographed on YMC Pack ODS column C18 (50×4.6 mm i.d., 3µ) using MeOH:Ammonium Acetate (2 mM) as binary gradient mobile phase at flow rate 1mL/min with splitter (1:1) over 5 min RT. Detection of analytes were performed on LC-MS/MS system in SRM mode. The method was validated over concentration range of 4.38-1121.35 ng/mL and lower LOQ was 4.38 ng/mL for the analyte. Recoveries from spiked controls were >83% for the analyte and IS at all QC levels. Within batch and between batch accuracy for Niraparib was found within 94.2-105.8% and 98.9-102.0%. Within batch and between batch precision for niraparib was found <11.2% CV at all concentration levels. This method was successfully applied to monitor PK profile of niraparib on oral and IV administration to rats.