The effect of methyl jasmonate (MJ) spraying on the chemistry of Brassica plants was investigated. Glucosinolates (GLS) in the leaves, stems, and roots of laboratory-grown oilseed rape (Brassica rapa subsp. oleifera cv. Tuli and Valo) 3 and 7 days after MJ treatment were analyzed. Volatile organic compounds (VOCs) from whole oilseed rape plants were collected 3 days after MJ treatment. GLS were also analyzed from field-grown oilseed rape (cv. Valo) treated with MJ. The production of indolyl GLS in laboratory-grown oilseed rape, especially the concentration of 4-hydroxy-3-indolylmethyl (4-OH-glucobrassicin) in leaves, stems, and roots, 3-indolylmethyl (glucobrassicin) in stems, and 4-methoxy-3-indolylmethyl (4-methoxyglucobrassicin) in roots, was induced after MJ treatment. The VOC emission profile changed after MJ treatment, and homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) was detected only in MJ-treated plants. The GLS concentration in the field-grown plants was significantly higher in MJ-treated plants than in control plants. These results suggest that spraying with MJ induces the production of secondary compounds, that is, GLS and VOCs, in Brassica plants. The induction of VOC emissions in oilseed rape is comparable to that caused by insect feeding damage. Thus, MJ-treated crop plants may become less palatable to insect herbivores and more attractive to natural enemies of herbivores.