In order to study the effect of soil nitrogen content and water hardness on glyphosate efficacy on common lambsquarter (Chenopodium album L.) and redroot pigweed (Amaranthus retroflexus L.) control, an experiment was carried out as a completely randomized design in a factorial arrangement with three replications. Experimental treatments were included soil nitrogen content (18, 50, 90, 200 and 300 mg/kg soil), glyphosate doses (0, 75, 100, 125, 150, 175 and 200 % glyphosate recommended dose for common lambsquarter (5 lit/ha) and redroot pigweed (3 lit/ha)), calcium carbonate concentration in water ( 0, 100, 300, 600 and 1200 ppm). Results showed that increasing water hardness decreased glyphosate efficacy in control of two weeds and increased glyphosate ED50 parameter. Minimum (1453.17 and 906 gr a.i ha-1 for common lambsquart and redroot pigweed, respectively) and maximum (3424.45 and 1606 gr. a.i ha-1 for common lambsquart and redroot pigweed, respectively) glyphosate ED50 was observed in 0 and 1200 ppm of water hardness respectively. Increasing soil nitrogen content from 18 to 300 (mg/kg soil) increased glyphosate efficacy in two weeds and glyphosate ED50 decreased from 3217.03 and 1745.2 to 1612.58 and 896.49 (gr. a.i ha-1) for common lambsquart and redroot pigweed, respectively. Based the results of this experiment, increasing water hardness, ghlyphosate efficiency decreased on weeds control and increasing soil nitrogen content can decrease the negative effect of water hardness on ghlyphosate efficacy.