Flos carthami (FC), also known as Carthamus tinctorius, is a traditional Chinese herbal plant that has been prescribed since centuries for treating various symptoms related to blood circulation improvement. This study aimed to investigate the effects of FC on calcium oxalate (CaOx) formation in ethylene glycol (EG)-fed rats. A total of 50 male Sprague-Dawley rats were divided into the following 6 groups: group 1, as the normal control (n = 5); group 2 received gastric gavages of starch and 0.75% EG (placebo, n = 5) as a stone inducer; group 3 (n = 10) received EG and potassium citrate as positive controls; group 4 (n = 10) received 0.75% EG and 300 mg/day FC; group 5 (n = 10) was treated with EG and 600 mg/day FC; group 6 (n = 10) received with EG and 1,200 mg/day FC. For all experimental animals, 24-h urine and blood samples were analyzed at the beginning and end of the experiment. Kidney tissue was histopathologically examined using a polarized light microscope, and crystal deposits were evaluated by a semi-quantitative scoring method; these scores were significantly lower in the FC groups (600 and 1,200 mg/day) than in the placebo group. Thus, FC administration appeared to inhibit the deposition of CaOx crystal EG-fed rats. We, therefore, consider that FC may be effective for preventing stone disease, albeit with certain side effects, such as a bleeding tendency. Further clinical trials are needed for evaluating its benefits and possible side effects.