Two types of recessive congenital methaemoglobinemia (RCM) is caused by NADH-dependent cytochrome b5 reductase enzyme de ciency encoded by CYB5R3 gene. RCM-I is characterized by higher methaemoglobin levels (>2 g/dL), causing only cyanosis, whereas RCMR-II is associated with cyanosis with neurological impairment. The present study discovered three novel homozygous pathogenic variants of CYB5R3 causing RCM I and II in four unrelated Indian patients. In patient-1 and patient-2 of are of RCM type I caused due to novel c.175C>T (p.Arg59Cys) and other reported c.469T>C (p.Phe157Ser) missense pathogenic variants respectively, whereas patient-3 and patient-4 presented with the RCM type II are related to developmental delay with cyanosis since birth due to a novel homozygous (g.25679_25679delA) splice-site deletion and novel homozygous c.824_825insC (p.Pro278ThrfsTer367) single nucleotide insertion. The CYB5R3 transcript levels were estimated by qRT-PCR in the splice-site deletion, which was 0.33fold of normal healthy control. The insertion of nucleotide C resulted in a frameshift of termination codon are associated with neurological impairment. This study can help to conduct genetic counselling and, subsequently, prenatal diagnosis of high-risk genetic disorders.