The qRT-PCR analysis of 139 clinical samples and analysis of 150 on-line databaseclinical samples indicated that AKT3 mRNA expression level was elevated in primaryprostate tumors. Immunohistochemical staining of 65 clinical samples revealed thatAKT3 protein expression was higher in prostate tumors of stage I, II, III as comparedto nearby normal tissues. Plasmid overexpression of AKT3 promoted cell proliferationof LNCaP, PC-3, DU-145, and CA-HPV-10 human prostate cancer (PCa) cells, whileknockdown of AKT3 by siRNA reduced cell proliferation. Overexpression of AKT3increased the protein expression of total AKT, phospho-AKT S473, phospho-AKT T308,B-Raf, c-Myc, Skp2, cyclin E, GSK3β, phospho-GSK3β S9, phospho-mTOR S2448, andphospho-p70S6K T421/S424, but decreased TSC1 (tuberous sclerosis 1) and TSC2(tuberous Sclerosis Complex 2) proteins in PC-3 PCa cells. Overexpression of AKT3also increased protein abundance of phospho-AKT S473, phospho-AKT T308, andB-Raf but decreased expression of TSC1 and TSC2 proteins in LNCaP, DU-145, andCA-HPV-10 PCa cells. Oncomine datasets analysis suggested that AKT3 mRNA levelwas positively correlated to BRAF. Knockdown of AKT3 in DU-145 cells with siRNAincreased the sensitivity of DU-145 cells to B-Raf inhibitor treatment. Knockdown ofTSC1 or TSC2 promoted the proliferation of PCa cells. Our observations implied thatAKT3 may be a potential therapeutic target for PCa treatment.