In this work, chemical activation was employed to produce activated carbons and assess the impact of phosphoric acid (H3PO4) on their physicochemical properties. Using Myrtus communis Leaves (MC-Leaves) as the precursor and varying H3PO4 impregnation ratios (30%, 60%, 100%, and 150wt.%). The activation was conducted at 450°C (10°C/min) for 1hour in a room atmosphere. The effects of H3PO4 were evaluated through various techniques, including BET surface area analysis, FESEM-EDS imaging, XPS, FT-IR-ATR, Raman spectroscopy, CHNS-(O) elemental analysis, and Methyl orange (MO) adsorption studies. The specific surface area (SSA) and total pore volume increased from 642m2/g to 1237m2/g, total pore volume increased from 0.29cm3/g to 0.97cm3/g, and the mean pore diameter increased from 1.9nm to 3.2nm by increasing the impregnation ratio from 30wt.% to 150wt.%. The pH(pzc) of MC-ACs exhibited an acidic character, owing to the presence of oxygen-containing functional groups such as hydroxyl, carboxyl, metaphosphate (-PO3-), phosphates, and pyrophosphate groups, as indicated by XPS and FT-IR analysis. At a room temperature of 22°C and an ideal pH of 2.06, the maximum adsorption capacity (qmax) rose from 46.02±4.63mg/g to 326.54±37.67mg/g as the impregnation ratio increased from 30wt.% to 150wt.%. Freundlich isotherm well explained the adsorption equilibrium at 22°C for all MC-ACs. The effect of temperature illustrates that the adsorption of MO onto MC-AC30% was endothermic, while the adsorption of MO onto MC-AC150% was an exothermic. The kinetic study was conducted at 22°C, when the equilibrium time was at 4hours, and it was a pseudo-second order (PSO) model.