HYPEROXALURIA is considered the real cause of the kidney oxalate stones. The present work is considered as an exploratory study which is continued with an original research work to evaluate the efficacy of the aqueous extract of Rosmarinus officinalis Linn on oxalate fragmentation in rat tissues. This work was divided into two different studies an in vivo study and an in vitro one. Rats in the in vivo study were divided into two groups: Group (1) represented the control group while in group (2) rats were injected with sodium oxalate to trace the oxalate impact and oxalate stones formation in rat tissues. The in vitro study was performed by adding sodium oxalate in human urine with or without the addition of different concentrations of the grinded leaves of Rosmarinus officinalis Linn. Results showed mild significant changes in some of the serum biochemical parameters in the oxalate treated group. On the other hand, the histopathological examinations showed that hyperoxaluria exhibited many tissue distortions in the kidneys, the bone marrow and the brain more than those found in the liver and the spleen compared to the control group. Oxalate crystals were noticed in rats' urine in the oxalate injected group and no stones were observed in kidneys or in other tested tissue. The in vitro study results showed that the plant leaves displayed highly fragmentation impact on oxalate crystals in human urine at a certain dose range concentration which when increased showed no effect on oxalate crystals fragmentation. It was concluded that Rosmarinus officinalis Linn had a great influence on oxalate fragmentation at a certain dose range.