This paper describes a fast and low-cost method for determination of melamine, an emerging environmental contaminant, in soil and sediment using ultrasonic-assisted extraction coupled with high performance liquid chromatography. The parameters used for sample pretreatment and chromatographic analysis were tested and optimized. The samples were extracted by 5% (v/v) ammonia in methanol with ultrasonic assistance for 5 min, followed by centrifugation and nitrogen blowing, without a cleaning procedure such as solid phase extraction. Chromatographic separation was achieved by a cyano column using acetonitrile/water (5/95, v/v) as the mobile phase containing no ion-pair reagent, and the quantification was carried out by an external standard method. An excellent linearity for melamine was obtained over the concentration range of 0.05–5 mg kg⁻¹ with a correlation coefficient of 0.9999. The limit of detection (S/N = 3) and the limit of quantification (S/N = 10) for melamine were 0.01 mg kg⁻¹ and 0.04 mg kg⁻¹, respectively. The recovery for melamine ranged from 95.0% to 105.9%, with relative standard deviations (RSDs) (n = 3) of 1.6–5.3%. The proposed method was shown to be simple, rapid, cheap, sensitive and accurate, and was applied to the analysis of melamine in soil and sediment samples with satisfactory results.