Heat treatment is the most suitable technique for altering the microstructure and, consequently, it is possible to create the optimal balance of corrosion resistance and mechanical strength in a material by carefully regulating the conditions during the heating process. The present work aims to investigate the effect of heat treatments (annealing) at (300°C) at different times (10, 20, and 30 hr) on the magnesium alloy. How the Mg17Al12 phase influences the corrosion behavior of AZ91D magnesium alloy was quantified in different solution (SBF, Lactic and Ringer). It was able to construct an extensive range of Mg17Al12 phase volume fractions by varying the annealing period. The corrosion potential of many specimens with varied proportions of the Mg17Al12 phase was evaluated. The results of the conducted tests manifested that the material's resistance to corrosion greatly improved with an increase in the volume fraction of Mg17Al12 phase. The effect of heat treatment on the microstructure was analyzed using transmission electron microscopy and X-ray diffraction. The SEM photographs evinced that the amount of β-Mg17Al12 phase decreased significantly, with the distribution occurring at the grain boundaries and with increasing the time of annealing, resulting in a highly saturated α-grain. The XRD validated the all material peaks of phases that are present. The corrosion test behavior of AZ91 alloy in the simulated body fluid (SBF), lactic, and Ringer solutions was investigated through electrochemical measurements, the result was elucidated as measured along the Tafel slope, and the corrosion current density of all heat treated samples was lower than that of the as-cast sample. The measurement of hardness (HV) demonstrated that the hardness decreased to (64.5 HV0.5) during the heat treatment. The result antibacterial efficiency was revealed that AZ91 at 30 hr was best then as cast against the bacteria E.coli.