Mealworms (Tenebrio molitor) have a great potential to serve as a sustainable food source for humans due to their favorable nutrient profile and low environmental impact. Feed formulation and optimization are important for mealworm production. The objective of this study was to evaluate the effects of fresh plant materials-supplemented diets on the growth performance and nutritional value of mealworms. Mealworm larvae were grown on wheat bran or wheat bran enriched with carrot, orange, or red cabbage for four weeks. Larval and pupal survival, growth rate, pupating rate, duration of pupal stage, proximate composition, reducing power, metal chelating activity, and radical scavenging activity of the mealworms were analyzed. Dietary supplementation with fresh plant materials did not result in significant changes in mealworm survival, development, proximate composition, or antioxidant activities. However, mealworm larvae fed on carrot-, orange-, and red cabbage-supplemented diets had improved growth rates, and were 40%–46% heavier in week four than those fed on wheat bran only, indicating the supplementation resulted in an increased production efficiency of mealworm larvae. Our findings may help optimize the diet formulation for mealworm mass production.