Recently, we reported an animal semiconductor PET with the spatial resolution of 0.8 mm FWHM within the central 20 mm-diameter of FOV for the purpose of biomedical study using rats and mice. This ultra high spatial resolution was obtained by the use of small CdTe elements of 1.1mm x 1.0 mm x 5 mm. The FOV of this PET is 64 mm in diameter and 26 mm in axis. We applied to observe small tumors in mouse and succeeded to 1 Q obtain [ F]FDG images of mouse mammary carcinoma of ~1mm size.