RRE decoys are short RNA oligonucleotides corresponding to the HIV Rev response element (RRE) sequence, which protect cells from HIV replication by inhibiting the binding of the HIV regulatory protein Rev to the authentic HIV RRE region. Previously minimal RRE decoy containing the 13-nucleotide primary Rev binding domain of RRE was described to be a potent inhibitor of HIV in CEM cells. In this report, we analyzed and compared the ability of a series of RRE decoy derivatioves to inhibit HIV replication in CEM cells to develop increasingly effective RRE decoy. Using an improved tRNA cassette to express high level of RRE transcripts in cells, we found that a variant form of stem-loop II(SLII) binding domain of wild type RRE termed RRE40 was more potent than any other RRE decoys previously developed or tested here and protected all cells most effectively from HIV. RRE40 was previously selected in vitro which binds to Rev protein 10-fold better than wild type RRE. CEM cells expressing RRE40 decoy RNAE40 decoys inhibit HIV specifically by sequestering Rev binding to the authentic RRE target in HIV RNA and indicated that RRE40 RNA identified by using in vitro binding studies also binds Rev in cells. These obserbations have important implications for experiments involving optimization of clinical application of RNA decoy based gene therapy protocol against HIV.