Abstract: J-integral of sheet notched specimen has the simplest form when the notched surface has been taken as the integral contour, i. e.it can be still simplifiedwhereandit can be seen that the ratio of J-integral to radius of curvature P is proportional to the maximum deformation work density W0 at notch root.The specimens were cut from hot rolled sheet of aluminium alloy LY12 with yield strength σ0.2=11.2 kgf/mm2. The specimen sizes are: thickness B = 30mm, width W= 150mm, notch depth a=40mm, and the radiuses of notch curvature ρ=20mm and 9mm, respectively. The resistance strain gauges of 1 by 1mm were adhibited on the inner surface of notch at angles θ being 0°, 10°, 20°, 30°, 45°, 60°, 75° and 90°, respectively. And then, the measurement of strain distribution ε（θ） at various load levels was made and deformation work density distribution W（θ） was derived from stress-strain curve. The value A, at last, has been determined by means of numerical integration and the approximation function, and varied in a range of 0.9 to 1.2.Owing to the limitation of the experimental accuracy and the difficulty in determining exact degree of plane strain, the agreement of experimental calibration of J-integral in the present work with J converted from equivalent stress intensity factor Keff considering Weiss's correction of plastic zone can be considered as an approximation for engineering.