MicroRNAs (miRNAs) are a class of highly conserved endogenous non-coding small RNAs crossing kingdoms of organisms. By searching known miRNAs identified from plant species against tomato nucleotide sequences, 13 pre-miRNAs of the nine mature miRNAs were found, amongst, six had been cloned. To confirm our prediction, a miRNA-detecting microarray was designed with probes complementary to all non-redundant mature plant miRNAs documented to date. After hybridizing with small RNAs extracted from tomato leaf tissue, 78 highly expressed mature miRNAs were detected, including all the miRNAs predicted above. Conformation of some miRNAs expression by Northern hybridization indicated that they were highly accumulated not only in leaf tissues but also in roots and stems. Additional BLAST searches with newly recognized miRNAs against tomato mRNAs from NCBI yielded 23 potential targets mainly associated with the phase change from vegetative to generative growth, with flower development and with responding to plant hormone and virus stress.