Nanoparticles and nanotechnology have been applied in agriculture, including for plant nutrition improvement, and pest control. Little research has been conducted on nano-calcium carbonate in plant protection and nutrition. In this study, we compared the effects of nano-calcium carbonate and colloidal calcium carbonate and found that nano-calcium carbonate treatments were better at increasing calcium content when sprayed on Tankan (Citrus tankan) leaves. Field tests on California red scale (Aonidiella aurantii) and Oriental fruit flies (Bactrocera dorsalis) both showed that nano-calcium yielded better control rates. Moreover, bioassays of Oriental fruit flies conducted using calcium carbonate particles yielded lower LC 50 values for nano-calcium. Additionally, nano-calcium performed better in terms of protection efficacy against oviposition punctures from Oriental fruit flies on the Indian jujube. Nano-calcium yielded better overall results than colloidal calcium for fertilization, plant protection, and pest control.