In recent years, chitin nanoparticles, especially the cationic form, have shown promising insecticidal activity on insect pests that threaten the world's food security. Though no extensive researches were done on the topic, all the reported findings agreed that the cationic nano chitin crystal alone or as a commercial insecticide carrier or by mixing with commercial insecticide has insecticidal activity and even reduces pesticide usage by up to 50%. The cationic nano chitin crystal also demonstrated excellent fungicidal activity against certain plant pathogens and enhanced plant immunity. This chapter presents the insecticidal role of chitin nanoparticles or crystals and their mechanism of action; the developed chitin nanoparticle syntheses and characterization techniques are also highlighted in the chapter.