This study investigates the effect of organic/inorganic nano-hybrid silica on the chloride penetration of cement mortar. This nano-hybrid silica was produced by using a starting material of sodium silicate, instead of using tetraethyorthosilicate or tetramethyl orthosilicate that is expensive, but still commonly used in the literature. Three mortar types (namely, control cement, slag cement and ternary cement) were prepared for this investigation. Blast furnace slag of 40 % was used for the slag cement, and blast furnace slag of 40 % and fly ash of 30 % were used for the ternary cement. Test results showed that the cement mortar with the proposed nano-hybrid silica improved compressive strength around 20 % higher than the control cement, 38 % higher than the slag cement and 19 % higher than the ternary cement. In addition, this study found that by replacing cement with this nano-hybrid cement of only 3% by volume, the percentage of chloride penetration was reduced to 30 %, compared to other specimens without the nano-hybrid silica, and the watertightness was improved to 24 %, compared to the ternary cement. In particular, the use of the nano-hybrid silica significantly reduced the porosity of cement ranging from 0.06 to 3.00 ${mu}m$.