Long chain lipid (LCL) based tamoxifen loaded nanostructured lipid carriers (Tmx-NLCs) meant to target intestinal lymphatic systems (ILSs) was developed and characterized previously. The aim of the present work was to evaluate in vitro efficacy of developed Tmx-NLC against breast cancer cell lines and to confirm the hypothesis of targeting ILS after single dose oral administration. In vitro anticancer activity of Tmx-NLC was assessed in human estrogen receptor expressing breast cancer cell lines viz. MCF-7 and ZR-75-1. The study revealed relatively improved activity for Tmx-NLC compared to free Tmx against MCF-7 cells. However, the activity was compromised against ZR-75-1 cells which could be attributed to its up regulation of MUC1 gene. Confocal and flow cytometric analysis revealed remarkable intracellular uptake of Tmx-NLC and its localization in nuclear and perinuclear region of cells. Tmx-NLC exhibited distinctly different pharmacokinetic profile compared to Tamoxifen suspension (Tmx-susp) and exhibited an increment in the bioavailability by 2.71-fold and prolonged the T1/2 by 7.10-fold. Moreover, detectable drug concentration in mesenteric lymph nodes justifies our hypothesis of targeting ILS and explains the major uptake of Tmx to occur via lymphatic system.