Analysis of serum brain-derived neurotrophic factor (BDNF) levels in Alzheimer's disease (AD), amnestic mild cognitive impairment (aMCI) and controls with BDNF gene polymorphism and cognitive function were investigated. The study recruited 63 AD patients, 15 aMCI and 63 age- and sex-matched healthy controls from All India Institute of Medical Sciences, New Delhi, India. Patients with AD (12268.3 ± 7099.9 pg BDNF/ml) and aMCI (10780 ± 4184.2 pg BDNF/ml) had higher serum levels than had the controls (9362.833 ± 5883.32 pg BDNF/ml). Significant difference in BDNF levels was not found between the three groups. No significant difference was obtained between BDNF genotype and allele distribution between AD patients, aMCI versus controls; genotypic frequency: Chi-square = 3.21; p-value = 0.20 and allelic frequency: Chi-square = 0.412, p-value = 0.521, df = 1 (AD vs controls); Chi-square = 1.63, p-value = 0.201, df = 1 (aMCI vs controls). In conclusion, val66met polymorphism and BDNF serum level between the three groups and genotype did not significantly affect the serum BDNF level or age, Mini-Mental State Examination score in AD and aMCI. Further studies are necessary to elucidate the kinetics and the potential role of serum BDNF as a marker of disease progression in AD patients.