The Brassicaceae family includes many economically important species that are grown worldwide and used mainly for vegetable oils. Sclerotinia stem and leaf rot, caused by Sclerotinia sclerotiorum, is a devastating disease that affects many Brassicaceae species and threatens their long-term productivity and profitability. There are currently no genetic sources known to have a high level of resistance to this pathogen. In this study, 338 accessions from 13 cultivated and wild Brassicaceae species, including 266 accessions from Brassica juncea, were evaluated for Sclerotinia rot resistance and stem physical strength attributes. Large variation of resistance was found in Brassicaceae, with maximum differences of 23.08- and 8.25-folds in stem and leaf resistance, respectively. B. juncea IC 589660, D. tenuisiliqua and S. alba SA 1 showed high level of resistance to stem rot while B. carinata HC 0214, B. juncea IC 589660, B. juncea IC 491160, B. juncea IC 73231, and B. juncea IC 491463 exhibited high level of resistance to leaf rot. These accessions showed significantly lower disease scores than the resistant control. Among all the evaluated accession, B. juncea IC 589660 is the only genotype exhibited high resistance to both stem and leaf rot and could prove useful for S. sclerotiorum resistance breeding programs. The lack of association between leaf lesion size and stem lesion length revealed separate genetic regulation for stem vs leaf resistance. While, significant negative correlation detected between stem lesion length, and stem physical strength attributing traits indicated that stem physical strength-mediated resistance (SPSMR) factors were responsible for Sclerotinia stem rot resistance in Brassicaceae. Hard and woody stem is a prominent resistance factor that could be targeted in durable resistance breeding programs against stem rot. These findings pave the door for further research into the molecular basis of SPSMR’s response to Sclerotinia stem rot in Brassica oilseeds and other hosts. Sclerotinia stem and leaf rot resistant accessions identified in this study will be of considerable benefit not only in increasing our understanding of resistance mechanisms across different Brassicaceae species, but also in generating resistant cultivars against Sclerotinia sclerotiorum.