This study aims to analyse the effects of carbon nanospheres (CNSs) on the in-plane shear properties of basalt fiber-reinforced epoxy composite laminate (BFR). The CNSs were obtained from an economical fibrous residue attained from the sago palm tree, which is known as biowaste sago bark. Hand lay-up method was used to fabricate the unidirectional basalt fiber-reinforced epoxy composite laminates. The epoxy resin was mixed with carbon nanosphere particles (i.e., 0.6 wt - 1 wt). In-plane shear tests have been conducted as per ASTM standards. In addition, emphasis on the microstructural investigation using Scanning Electron Microscopy (SEM) is given, in order to study the fracture surfaces of the composite laminates. The results demonstrated significant improvement in in-plane shear strength when carbon nanosphere particles were included in the basalt fiber-reinforced epoxy composite laminate. The best result was obtained at 1.0 wt CNSs. It displayed an increment of 37.1 in in-plane shear strength, and 36.4 increment in modulus of rigidity, respectively, in comparison to neat basalt fiber-reinforced epoxy composite laminate. The improved accomplishment of CNSs/basalt fiber-reinforced epoxy composite laminate is due to good distribution of CNSs particles in the epoxy matrix. © 2018 Institute of Physics Publishing. All rights reserved.