ABSTRACT Early diagnosis of trichinellosis is still difficult because of the lack of specific symptoms and limited window for serological detection. Here we established an assay based on tracing phosphate ions generated during loop-mediated isothermal amplification (LAMP) to detect Trichinella spiralis DNA in rat feces during its early stage of infection. By targeting a 1.6-kb repetitive element of Tri. spiralis , the assay was able to detect Tri. spiralis DNA in the feces of all infected rats as early as 1 day postinfection (dpi). The positive detection lasted to 7 dpi in the rats infected with 250 muscle larvae, and 21 dpi in the rats infected with 5,000 larvae. The assay was highly sensitive, and could detect 1.7 femtograms (fg) of Tri. spiralis DNA with high specificity, and with no cross reactivity with the DNA from Anisakis pegreffii , Gnathostoma spinigerum , Angiostrongylus cantonensis , Enterobius vermicularis , Schistosoma japonicum , and Trypanosoma evansi . Our present study provided a reliable technique for the early diagnosis of trichinellosis with the advantages of simplicity and speed, as well as high sensitivity and specificity.