Glass fiber-reinforced plastics are an important composite material in the marine, automotive, and military industries due to their excellent mechanical properties, such as high strength, corrosion resistance and lightweight. This study aims to determine the effect of the number of glass fiber layers on the hardness of glass fiber/polyester composite materials. Random chopped strand mat glass fibers with a mass per unit area of 450 g/m² were used to prepare samples using the hand layup technique. The number of layers varied between 3 to 6 layers. The thickness of all samples is 3 mm. The Vickers microhardness device is used to measure the hardness, with a load of 50 g applied for a dwell time of 15 s. The results indicated that when increasing the number of glass fiber layers decreases the hardness values. The sample of three-layer listed the highest hardness value of 14.34 HV, while the values for the four-layer sample decreased to 11.42 HV, the five-layer sample to 9.72 HV, and the six-layer sample had the lowest value of 7.7 HV. This decrease in hardness is attributed to the increased number of interfaces between layers, which may lead to the appearance of weak points or air voids that affect the mechanical properties of the composite material.