The objective of this study was to assess the effect of fertilization (organic or synthetic) and cabbage, Brassica oleracea L., cultivars (‘K-Y cross’ and ‘Summer Summit’) on the chemistry of cabbage and on the responses of a cabbage specialist Pieris rapae crucivora Boisduval. Cabbages were grown from seeds in the greenhouse with either organic, synthetic, or no fertilizer treatments. Trials of ovipositional preference and larval feeding were conducted to evaluate the effect of foliage quality on insect responses. In addition, the foliar chemistry (water, nitrogen, total nonstructural carbohydrates, sinigrin, and anthocyanin) was measured during the insect bioassays. The results indicated that butterflies preferred to lay eggs on foliage of fertilized plants. The larvae grew faster on plants fertilized with synthetic fertilizer, but there was no evidence that contents of sinigrin delayed the developmental time of the larvae. However, plants that received organic fertilizer had higher biomass. In summary, the results of this study suggested that proper organic treatment can increase a plant's biomass production and may have a lower pest occurrence.