We are currently developing a small animal PET using CdTe detector arrays. Because of a semiconductor, the CdTe detector can be miniaturized to obtain a high spatial resolution of the PET. We examined the performance of the multi-strip CdTe detector array, which consists of 32 ch strips with detector size 1.2 × 1.15 × 4.5mm3, sensitivity for 511 keV annihilation photons, polarization for signal output and so on. To investigate the feasibility of ultra high spatial resolution of small animal PET by using the CdTe detector arrays, a prototype of small PET using the multi-strip CdTe detector arrays was manufactured, which consists of the two detector arrays faced each other by 100mm and can be rotated by stepping motor. The measurement of spatial resolution was performed by a small phantom of acrylic cylinder with 3cm diameter in which hot spots of 18F with 0.5mm diameter were placed with intervals of 2mm, 1.5mm and 1mm. We obtained a high resolution of 0.9mm FWHM. This results that the multi-strip CdTe detector array is enough to be used to a small high resolution PET.