Andrographis paniculata is traditionally used for many diseases and scientifically proven for anti-cancer property. Andrographolide which is the marker compound is believed to be the main contributor to the pharmacological activities. The poor solubility and bioavailability of this diterpenoid lactone could be overcome by nanoencapsulation. Reflux extraction, and followed by successive Soxhlet fractionation were used to obtain andrographolide rich extract from the herb. Spontaneous emulsion solvent diffusion was used to nanoencapsulate andrographolide using poly(lactic-co-glycolic acid) with 1% polyvinyl alcohol as emulsifier. Nanospheres loaded with andrographolide was found to have the particle size, 163 nm; polydispersity index, 0.26 and zeta potential, - 57.85 mV. The encapsulation efficiency and in vitro drug release were 80.0% and 84.2%, respectively. The andrographolide nanoparticles could inhibit the proliferation of cervical and neuroblastoma cells with no adverse effect on normal human skin cells. Andrographolide rich extract loaded nanoparticles could inhibit the proliferation of HeLa and SH-SY5Y cells, mainly through Bax-induced apoptosis. The result was consistent with the low expression of anti-apoptotic genes (Bcl-2 and Bcl-xL) and prognostic factor (Ki-67). The tumour size of HeLa bearing mice was significantly reduced (73%) after treated with andrographolide rich nanoparticles (10 mg/kg body weight) for a month.