Radiotherapy (RT) plays a prominent role in the treatment of prostate cancer (CaP) alone or as an adjuvant therapy. However, radioresistance is a major challenge in CaP RT. This thesis provides an overview of the literature regarding the mechanisms of CaP radioresistance, radiosensitisers research as well as radioresistance-related biomarkers discovery using proteomic approaches. The aims of the study were to: 1) investigate the roles and association of epithelial-mesenchymal transition (EMT), cancer stem cells (CSCs) and the PI3K/Akt/mTOR signalling pathway in CaP radioresistance; 2) identify proteins involved in CaP radioresistance using liquid chromatography tandem mass spectrometry (LC-MS/MS), validate the identified potential proteins and perform functional study; 3) investigate the therapeutic potential of combination therapy with PI3K/mTOR inhibitors and RT in CaP-radioresistant (RR) cell lines; 4) investigate the therapeutic potential of combination therapy with a PI3K/mTOR dual inhibitor BEZ235 and RT in CaP-RR tumour xenografts. I developed three novel CaP-RR cell lines (PC-3RR, DU145RR and LNCaPRR) by fractioned RT and found enhanced EMT/CSC phenotypes, activation of cell cycle checkpoints, autophagy, DNA repair as well as the PI3K/Akt/mTOR pathway and inactivation of apoptosis proteins in these cell lines. I identified 19 potential proteins in three paired CaP cell lines using LC-MS/MS proteomics. I also chose one identified potential protein marker-ALDOA for functional study and demonstrated that the depletion of ALDOA combined with RT effectively increased radiosensitivity in CaP-RR cells. In in vitro study, I found, in comparison with the combination of single PI3K or mTOR inhibitors and radiation, low-dose of dual PI3K/mTOR inhibitors combined with radiation greatly improved treatment efficacy. I also established PC-3-luc (from PC-3 by transduction) and PC-3RR-luc (from PC-3-luc cell line using fractioned radiation) tumours in subcutaneous (s.c) and orthotopic mouse models, and demonstrated BEZ235 combined with RT could significantly reduce tumour growth compared with RT or BEZ235 alone or vehicle control in PC-3RR-luc s.c and orthotopic models. Collectively, findings from my PhD study suggest that CaP radioresistance is related to by multifactorial traits especially associated with EMT, CSCs, PI3K/Akt/mTOR and other signalling pathways. Targeting these proteins or signalling pathways is promising for CaP radiotherapy to overcome radioresistance.