Noroviruses (NoVs) are members of the family Caliciviridae and are emerging enteric pathogens of humans and animals. So far, porcine NoVs have been detected exclusively in fecal samples from adult swine without clinical signs. Here we report the genome sequence of a NoV strain isolated from piglets with diarrhea. Experimental infection of miniature pigs with this porcine NoV-positive fecal sample confirmed that this strain can cause diarrhea in piglets. A phylogenetic tree based on the predicted amino acid sequence of the complete capsid region showed that this strain is separate from known porcine GII strains (GII-11, GII-18, and GII-19), constituting the sole member of a new branch.