Micro-porous magnetic activated carbon was prepared under ultrasonic irradiation as an adsorbent for dispersed solid phase extraction of dimethyl methyl phosphonate from water samples, before analysis by gas chromatography-ion mobility spectrometry. The magnetic activated carbon was synthesized and characterized by using a vibrating sample magnetometer, Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction techniques. Then, the effects of the amount of sorbent, extraction time and pH of the sample in the dispersive solid phase extraction method were investigated and optimized by the response surface method. The dispersion of 20 mg adsorbent powder in a 50 mL water sample for 5 minutes with chloroform as the desorption solvent showed an average recovery value of 95% for dimethyl methyl phosphonate. Afterward, the method was used successfully for the determination of dimethyl methyl phosphonate in river and spring water. The linear range was obtained to be 0.05-1 μg mL-1. The limit of detection and the limit of quantification were obtained to be 0.02 μg mL-1 and 0.05 μg mL-1 respectively. The analysis also showed good reproducibility with a relative standard deviation value of 3.1%. This method was shown to be easy, fast, reliable, and inexpensive.