An N-acylpiperazine derivative or a salt thereof in accordance with the present invention is represented by the following formula 1: ##STR1## wherein R.sub.1 represents a lower alkyl, hydroxy lower alkyl, lower acyl, or arylcarbonyloxy lower alkyl group; R.sub.2 represents hydrogen atom or a lower alkyl, lower alkoxy, lower alkenyl, amino, or nitro group; R.sub.3 and R.sub.4, which are identical to or different from each other, represent hydrogen atoms, halogen atoms, or cyano, nitro, lower alkyl, or lower alkoxy groups; and n represents 0 or 1. The N-acylpiperazine derivative has anti-ulcer effect or an antibacterial activity against Helicobacter pyroli to be available for prevention or cure of ulsers.