The characteristics of static earth pressure of cement treated sand were investigated by model experiment. Model grounds were constructed in the model tank by pouring the treated sand which were prepared by mixing 0%, 1%, 3% and 5% of cement, respectively, with Niigata East Port Sand. The earth pressures were measured with earth pressure gauges and load cells installed on the model wall. The applicability of Rankine's earth pressure theory was examined by comparing the measured earth pressures and theoretical ones. The active earth pressure of trated ground may be estimated by Rankine's earth pressure theory taking the internal friction angle and cohesion of treated ground into account. Rankine's theory, however, overestimates the active earth pressure of treated groung by 2.5 times, when the ratio between the unconfined compressive strength of treated ground qu and surcharge q, qu/q, becomes approximately equal to 1.