A new type of optical sensor based on electrospun composite polycaprolactam (N6)-dimethylglyoxime (DMG) nanofibers collected on a glass slide was fabricated. The nanofibrous mat was then impregnated with a polyvinyl alcohol (PVA) solution to make it transparent. The colorimetric sensor, N6-DMG@glass, was coupled with absorbance spectrophotometry for analytical determination of nickel ions (Ni2+) as red Ni(DMG)(2) complex. The main factors affecting performance of the sensor including DMG dosage, electrospinning time, polymer solution flow rate, electrospinning voltage, and PVA amount were investigated. Under the optimal conditions, limit of detection, limit of quantification, linear dynamic range, and determination coefficient (R (2)) were 2, 5, 5-100 A mu g mL(-1) and 0.9989, respectively. The relative standard deviation (%, n = 3) at the concentration level of 50 A mu g mL(-1) was 3.1 %. The technique was applied successfully to the determination of Ni2+ in electroplating nickel pool, tap water, and laboratory wastewater.