The immobilisation of enzymes is important for applications in bioelectrochemistry such as biosensors or biofuel cells. In this paper we report the immobilisation of lactate dehydrogenase (LDH) on poly(aniline)-poly(acrylate) [PANi-PAA] and poly(aniline)-poly(vinylsulfonate) [PANi-PVS] composite films. Two genetically engineered forms of LDH (E.C.1.1.1.27) from Bacillus stearothermophilus, one with a poly(histidine) tag on the C-Terminus (LDH-CHis) the other with a poly(histidine) tag on the N-terminus (LDH-NHis), together with the wild type enzyme (WT-LDH) were studied. The LDH-CHis and LDH-NHis both have better affinity for the poly(anitine)-poly(anion) composite films than the WT-LDH. The immobilised LDH reduces the coenzyme NAD(+) to NADH and oxidises the substrate, L-lactate, to pyruvate. The NADH produced is then oxidised at the poly(aniline)-poly(anion) composite films. The effects of buffer concentration, temperature, NAD(+) concentration, enzyme immobilisation conditions, film thickness and electrode rotation rate on the catalytic current were all investigated.