Earthworms being the allies of farmers increasing the porosity and fertility of agricultural soil. The current work was to investigate the diversity of earthworm along with the effect of Lead (Pb) toxicity on earthworms in the paddy fields of Assam. Being the biodiversity hotspot, there is a keen interest of the researchers to explore the cryptic, novel earthworm species in the paddy fields. The current exploration reveals eight different species of earthworm with accession number Eudrilus eugeniae (OP999656); Metaphire nanaoensis (OQ073567), Polypheretima elongata (OR053673), Perionyx depressus (OQ073568), Amynthas morrisi (OR518282), Amynthas phaselus (OR518347), Metaphire formosae (OR518417) and Eudrilus eugeniae PBP (OR053675) belonging to two dominant family Megascolecidae and Eudrilidae. The Shannon diversity index (H’) was found to be 2.045. These open up into a new heterogeneity and more integrated approaches is required to explore the unknown which is yet to discovered in the near future. Acute toxicity was evaluated using filter paper test with an endogenic earthworm Metaphire nanaoensis exposed to heavy metal Lead (Pb) with LC₅₀ found to be 0.5462 mg/ml. Morphological changes like swelling of body, mucous secretion was observed when exposed at highest concentration of 0.1mg/ml of Pb. The growth was seen to be minimum at 100 ppm on 25^th day of Pb exposure which were significantly less (p<0.05) in soil toxicity test. This would help in assessing the toxic potential of Pb and environmental impact with such heavy metal.