Phytopathogens, such as phytopathogenic bacteria, fungi, and nematodes, have caused great losses of crops every year, seriously threatening human health and agricultural production. Moreover, marine-derived fungi are abundant sources of structurally unique and bioactive secondary metabolites that could be potential candidates for anti-phytopathogenic drugs. One new sulfoxide-containing bisabolane sesquiterpenoid aspersydosulfoxide A ( 1 ) and nine known analogues ( 2 - 10 ) were isolated from the marine-derived A. sydowii LW09. The absolute configuration of the sulfur stereogenic center in 1 was determined by electronic circular dichroism (ECD) calculations. Compound 5 showed inhibition activity against Pseudomonas syringae , with a minimum inhibitory concentration (MIC) value of 32 μg/mL, whereas, compounds 2 , 7 , and 8 showed antibacterial activities toward Ralstonia solanacarum , with the same MIC value at 32 μg/mL. Meanwhile, compounds 3 , 7 , and 8 inhibited the fungal spore germination of Fusarium oxysporum , with the half maximal effective concentration (EC 50 ) values of 54.55, 77.16, and 1.85 μg/mL, respectively, while compounds 2 , 3 , 7 , and 8 inhibited the fungal spore germination of Alternaria alternata , which could be induced by vacuolization of germ tubes, with EC 50 values of 34.04, 44.44, 26.02, and 46.15 μg/mL, respectively. In addition, compounds 3 , 7 , and 8 exhibited nematicidal activities against Meloidogyne incognita second-stage juveniles (J2s). In addition, compound 8 possessed the strongest nematicidal activity of nearly 80% mortality at 60 h with the half lethal concentration (LC 50 ) values of 192.40 μg/mL. Furthermore, compounds 3 , 7 , and 8 could paralyze the nematodes and then impair their pathogenicity.