With recent advances in science and technology, there is a worldwide demand for lightweight, environmentally friendly, low-cost polymer composites. Basalt fiber-reinforced composites have received a lot of interest since they are less expensive, have good chemical stability, and have better mechanical properties than glass fiber. The present study is concerned with the effect of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs) on the mode I fracture behavior of basalt fiber-reinforced epoxy composites. The composites are fabricated by conventional hand layup with vacuum bagging technique and the mode I energy released rate \(G_{{{\text{IC}}}}\) is evaluated using a double cantilever beam test with three different MWCNTs contents of \(0.125,\) \(0.25,\) and \(0.5\%\) per weight of epoxy/hardener. It is observed that the fracture toughness increased proportionally with the addition of MWCNTs till \(0.25\% .\) The enhancement is primarily due to improved dispersion and interfacial adhesion between the epoxy resin and the MWCNTs. However, the interfacial characteristics for \(0.5\%\) of MWCNT might be diminished due to the agglomeration of MWCNTs in the epoxy resin. The finite element modeling (cohesive zone) correlates well with the experimental results and confirms the enhancement of interlaminar fracture toughness by adding MWCNTs.