Signals of QCD instanton-induced processes are searched for in neutral current deep- inelastic scattering at the electron-proton collider HERA in the kinematic region defined by the Bjorken-scaling variable x > 10−3, the inelasticity 0.2 < y < 0.7 and the photon vir- tuality 150 < Q2 < 15000 GeV2. The search is performed using H1 data corresponding to an integrated luminosity of 351 pb−1. No evidence for the production of QCD instanton- induced events is observed. Upper limits on the cross section for instanton-induced pro- cesses between 1.5 pb and 6 pb, at 95% confidence level, are obtained depending on the kinematic domain in which instantons could be produced. Compared to earlier publica- tions, the limits are improved by an order of magnitude and for the first time are challenging predictions.