A simple, precise and gradient RP- HPLC method has been developed and validated for Aciclovir raw and in tablet formulation. The proposed method was validated to obtain official requirements including accuracy, linearity, precision, selectivity and stability. The estimation was developed on C(18) column reversed-phase using the mobile phase composition as Phosphate buffer: methanol in the ratio (60:40 %. v/v). 1ml /minute was the flow rate and the maximum absorption were observed at 290 nm using Shimadzu SPD-20A Prominence UV-Vis detector. Aciclovir showed a precise and good linearity, the concentration range was 5-25 μg/mL. The RP-HPLC, assay showed the highest purity ranging 99.59 to 100.97% for Acyclovir tablet formulation. 100.19 % was the mean percentage purity. The Aciclovir retention time was found to be 3.01 minutes. The method accuracy was showed by statistical analysis.