Concerning sustainability and recycling considerations, geopolymers have recently raised as one of the most active alternatives to the current cement-based composites, in addition to that, the existence of fibers in any binding matrix yields a significant improvement in the behavior of the matrix. On the other hand, using waste materials in the binding matrices fulfills one of the main aims of sustainability, namely reusing wastes. In this concern, the previous research attempts focused on the effect of using fibers and wastes separately and hence using them together in one matrix is not clearly highlighted. The main objective of this study was to examine the engineering properties of metakaolin-based geopolymer mor- tars in the case of colemanite substitution up to 30% and basalt fiber of different lengths. In the 10 series produced, firstly 7th day and 28th day compressive and flexural strengths, UPV, abrasion resistance test, porosity, unit weight, and water absorption results were examined. As the durability tests, 90 cycles of freezing-thawing between 20 and +20 C, high-temperature tests of 250, 500 and 750 C were applied. Also, geopolymer samples were exposed to 10% Hydrosulfuric Acid (H2SO4) for 3 months. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Thermogravimetric/Differential Thermal Analysis (TGA-DTA) analyses were performed at the end of the durability tests. The results showed that in the case of 10% colemanite substitution, it increased the compressive strength results and lowered it at higher rates. With a colemanite substitution of 10%, the compressive strength results of 28 days increased by 1.71%, and in the case of 20% and 30% coleman- ite substitution, there was a decrease in the compressive strength of 13.64% and 26.99%, respectively. The compressive strength results showed that 24 mm long basalt fiber reinforced samples had better results than 12 mm long basalt fiber reinforced samples. It was seen that geopolymer specimens maintain sta- bility in freezing-thawing, elevated temperatures, and sulfuric acid effects.