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Black rot is a destructive disease that affects <i>B. oleracea</i> crops, causing significant losses to growers throughout the world. The purpose of this study was to screen out new sources resistant to <i>Xanthomonas campestris</i> pv. <i>campestris</i> race 4 (<i>Xcc</i>4) in 26 cauliflower and six related wild species, and to assess the inheritance of resistance. The results indicate that most of the tested accessions were susceptible or had intermediate resistance, except the Boc4601 (a cauliflower stable inbred line) and PI435896, UNICT5168, and UNICT5169 (wild accessions). Among them, UNICT5169 (<i>Brassica montana</i>) and PI435896 (<i>Brassica balearica</i>) showed the strongest resistance to <i>Xcc</i>4, with significantly lower disease index (DI), area of the infected part (AIP) and proportion of the infected part to the total leaf area (PTL) values. UNICT 5169 was selected as an <i>Xcc</i>4-resistant parent because of its relatively good cross seed-setting rate with cauliflower cultivars. F₁ hybrids were successfully produced between this wild resistant accession (UNICT 5169) and one susceptible cauliflower breeding line (Boc3202-4), indicating the potential transferability of this resistance to cauliflower. The results of the symptoms severity evaluation of the F₂ population indicate that <i>Xcc</i>4 resistance in UNICT5169 is a quantitative trait, which guides future resistance gene location and black rot resistance breeding.