At 300 K and between 0~13.3 kPa, adsorption isotherms for O2, CO, CH4 on porous palladium were measured by using PVT method in low-vacuum system. The results indicate that Adsorption isotherms for CO on Pd is identical with the type adsorption isotherms that the amount adsorbed of CO increases with increasing pressure(<2.6 kPa), but little additional CO adsorbs with pressure increasing(<13.3 kPa). Isotherm for adsorption of O2 or CH4 has a different effect in contrast to CO, i.e. significant adsorption of O2 even at low pressure (<100 Pa), and the isotherms doesn’t saturate at higher pressure(<13.3 kPa), and the amount adsorbed of CH4 is little and increases slightly with equilibrium pressure rising sharply (<13.3 kPa). And isotherm for adsorption of CO or CH4 can been classified Longmuir adsorption type, and that of O2 can been described by Longmuir adsorption model only when equilibrium pressure is less than 1.33 kPa