【Aim】 The fall armyworm,Spodoptera frugiperda, is a major invasive pest that has recently entered China. Investigating the anatomical structures of the larval internal organs of S. frugiperda can provide foundational knowledge for physiological study and control against this pest. 【Method】 The internal organs of the fifth-instar larvae of S. frugiperda were dissected, observed, and photographed under a deep-field stereo-microscope. 【Result】 The primary internal organ systems of S. frugiperda larvae include the digestive system, central nervous system, excretory organs, and respiratory system. The digestive system consists of the alimentary canal, silk glands, and salivary glands, with the alimentary canal comprising the fore-gut, mid-gut, and hind-gut. The central nervous system is composed of a pale red brain and a ventral nerve cord with 12 pairs of ganglia, with the last two pairs of abdominal ganglia being close and fused. The primary excretory organs, the Malpighian tubules, are located on both sides of the posterior end of the alimentary canal, with 3 tubules on each side, totaling six, and appear yellow and transparent. The respiratory system consists of spiracles and tracheae, with 9 pairs of functional spiracles distributed on the prothorax and abdominal segments 1-8 of each larva. Each spiracle internally contains a closing bow, a closing band, and a closing rod. The tracheal system is composed of main tracheae and branch tracheae of varying thicknesses, with the tracheal intima locally thickened to form helical filaments to enhance the tracheal resilience. 【Conclusion】 The composition and distribution of the internal organ systems inS. frugiperda larvae are similar to those of other lepidopteran insects. This result can lay a foundation for the study of insecticide targets and mechanisms.