Glass fibers are the most commonly fibers used in the manufacture of composite structures. Their good mechanical properties and low price resulted in a vast usage of glass fibers compared to carbon, aramid and basalt fibers. Also alkali-resistant glass fibers are widely used in the manufacture of composites which are used in aggressive and corrosive environments. The purpose of this study is to improve alkaline resistance of E-glass fibers, which is the most common glass fibers, by using two methods: coating with ZrO 2 nanoparticles () (dip-coating method) and deposition of Ni-P and Ni-P-Nano-ZrO 2 by electroless coating. The alkaline aggressive resistance of the samples was investigated by weight loss measuring. The results indicated that alkaline weight reduction of E-glass fibers coated with ZrO 2 using dip-coating method was decreased by increasing the concentration of up to 25 wt% and it was increased at higher concentrations due to accumulation of . Based on the obtained results, decreasing coating rate caused a slightly decrease in coating layer thickness and increase in alkaline weight loss due to the domination of gravity forces on viscous forces at lower coating rates. Results also indicated that post-treatment of samples after coating at 600? tends to fix a uniform coating with more and denser ZrO 2 layer and therefore the fibers had higher alkaline resistance. Based on the results of dip-coating method, the best coated sample with the lowest alkaline weight loss was obtained by the ZrO 2 sol concentration of 25 wt% and coating speed of 1500 mm/min. Electroless coating results showed that alkaline weight reduction for the deposited Ni-P-nano-ZrO 2 glass fibers was improved compared to the Ni-P coated samples because caused disturbance in the formation of the passive layer. In comparison of two common recipes for metals and non-metals electroless coating, it was observed that the samples coated using metals recipe had higher alkaline resistance than the other recipe, due to the acidic pH and greater phosphorus content. Therefore, it was concluded that optimum alkaline weight loss was obtained using the electroless coating of the fibers using the metals recipe. Key words Glass fiber, Coating, Dip-Coating, Electroless, Alkaline Resistant, ZrO 2 , Nanoparticles