Pre-breakdown currents through the poly (ethylene-co-butyl acrylate) (EBA) nanocomposites filled with spherical alumina particles were studied as a function of particle coating and moisture content. The nanocomposites were prepared from a mixture of EBA formulations (13 wt% butyl acrylate groups content) and alumina powder. Two kinds of alumina nanoparticles were used: NA (25 nm in diameter) and ND (45 nm in diameter). The particles were either unmodified or surface-treated with aminopropyltriethoxy silane or octyltriethoxy silane. Two different relative humidities of air were used for conditioning the samples prior to testing: 0 % RH (dry case) and 86 % RH (samples were saturated with moisture). The pre-breakdown current measurements were performed with a DC ramp of 1.2 kV/s. Twenty samples were tested for each material formulation -ten of which were tested in dry conditions and ten were tested after conditioning in humid environment. Results were compared to the reference unfilled EBA samples. The measured currents were analyzed under the assumption of space charge limited conduction. As expected, conditioning materials in humid environment caused an increase in pre-breakdown currents. This effect was more pronounced for nanocomposite materials, while the reference unfilled material was least affected.