In the present research, electroless Ni-P deposits were obtained on Al5083 substrate. The effects of coating time, substrate roughness, heat treatment temperature and heat treatment time on morphology, phosphorus content, structure, microhardness, adhesion and corrosion behavior of the deposits in 3.5 wt.% NaCl solution were investigated. Deposits were heated at temperatures ranging from 200 to 400 °C for 1-4 h. Surface morphology of the coatings exhibited a nodular feature with a typical cauliflower-like structure. By increasing thickness of coatings, the phosphorus content of surfaces decreases but the number of porosities decreases and the corrosion resistance increases. Also the corrosion resistance of electroless deposits on smooth substrate in comparison with rough substrate is better. The structural characterization was done by means of X-ray diffraction studies. As-deposited coating exhibit broadened X-ray reflections indicative of a semi-amorphous structure. Heat treatment decreased the amorphous phase and the final equilibrium phases were Ni 3 P and Ni crystals within the nanocrystalline size range. The results of Vickers microhardness testing showed that the maximum hardness was achieved for the samples which have been heat treated at 400 °C. This is caused by the formation of intermetallic Ni 3 P stable phase at this temperature, acting as a function of precipitation hardening. Corrosion resistance of the coatings indicated that on heating to 240 °C, the corrosion resistance increased and then reduced at higher temperatures. Heat treatment at 400 °C leads to crystallization of the amorphous phase, making available more number of grain boundaries which are highly prone to corrosion attack. Therefore, the heat treatment of electroless specimens at 400 °C significantly decreases their corrosion resistance. Also evaluation of the corrosion behaviour coatings which heat treated at 240 °C and 320 °C temperatures and longer times indicated that by increasing heat treatment time, no considerable decreasing in the corrosion behaviour observed until the formation of Ni 3 P intermetallic phases. For evaluation of susceptibility to localized corrosion, cyclic potentiodynamic polarization method is used. All of the curves of the electroless coatings exhibit positive hysteresis. Positive hysteresis occurs when the passive film is unable to repair breakdown at localized areas and pits initiate and continue. For evaluation electroless coatings adhesion to substrate, bend test is used according to B 571-97 standard. All of the electroless coatings aren’t peeled in bended area and aren’t separated from substrate even by insertion of a sharp probe at the interface of the coating and substrate that exhibit good adhesion coatings t