One of the most common types of cancer is lung cancer, which frequently manifests as locally progressed or metastatic illness at the time of diagnosis. Adults with metastatic Non-small Cell lung cancer (NSCLC) that is ALK-positive should take ALECINIB. In order to assess Alectinib, we created and verified an isocratic high-performance liquid chromatography method in this work. Drug quantitation and selectivity are possible using this approach. A passive Cosmoil C18 analytical column (4.6 X 150 mm, 5 μm) was used to validate the procedure. The equilibration phase included methanol and water (80:20% v/v) at a pH ratio of 3. The temperature of the column was kept at room temperature, and the flow rate was 1 mL/min. The wavelength of the photodiode array detector was adjusted to 267 nm. In the concentration range of 10, 20, 30, 40, and 50 ppm, the calibration curve is linear, and the correlation coefficient (r2) is 0.999. The percentage RSD for intra- and inter-day precision was 0.189 and 0.106%, respectively. The limits of detection (LOD) and quantification (LOQ) were determined to be 0.0747 μg/mL and 0.2264 μg/mL, respectively. The precision, accuracy, linearity, precision, limit of detection, quantification, and technique strength are all validated for this approach. This method can be utilized for Alectinib analysis and estimate in active pharmaceutical and medications because of its accuracy and speed. Stress degradation for Alectinib was carried out and it showed degradation in every condition. It showed higher degradation in base hydrolysis with upto 23.64 % degradation and upto 17.04% degradation in Acidic condition. In the oxidation condition, heat degradation and Photolytic conditions the degradation was found to be 8.79%, 1.08% and 0.14% respectively.