Sulforaphane is an anticarcinogenic isothiocyanate derived from 4-methylsulfinylbutyl glucosinolate (glucoraphanin), which is abundant in broccoli (Brassica oleracea var. italica) florets. However, some breakdown products from alkenyl glucosinolates present in many broccoli cultivars, particularly oxazolidine-2-thione hydrolyzed from 2-(R)-hydroxy-3-butenyl glucosinolate (progoitrin), have potentially harmful effects on human and animal health. The main objective of this study was to improve the glucoraphanin concentration in F1 hybrids by cross-breeding with inbred lines and doubled haploids. Glucoraphanin concentrations in 31 of the 61 F1 hybrids were significantly higher (P = 0.05) than that of the commercial cultivar (Youxiu) with the highest concentration of glucoraphanin (4.18 μmol·g−1 dry weight) among eight reference cultivars. Sixteen of the F1 hybrids had glucoraphanin concentrations 3-fold higher than that of ‘Youxiu’. Alkenyl glucosinolates were not detected in the new hybrids as a result of the parents having few of these compounds but were found in five reference cultivars. Most F1 hybrids showed moderate indole glucosinolate concentrations and acceptable commercial traits. IL609 and IL702.2 were determined to be promising parental lines as a result of the high glucoraphanin concentration that they and their offspring contained. The findings also indicated that some F1 hybrids do not show the high-glucoraphanin character of their parents; consequently, evaluation of these F1 hybrids for their glucosinolate content is required for breeding high-glucoraphanin broccoli.