Development of new antimicrobials for drug-resistant Acinetobacter baumannii is urgently needed. 4H-4-oxoquinolizines were screened against A. baumannii ATCC 17978 by HTS analysis. Novel 4H-4-oxoquinolizines were extremely active against XDR A. baumannii isolates. Novel 4H-4-oxoquinolizines were active against fluoroquinolone-resistant A. baumannii.