Abstract: Failure analysis of a light bus engine crankshaft was carried out by macro observation on fracture surface, chemical composition analysis, microstructure examination, property testing and finite-element analysis. The results show that the radius of arc transition between the neck of connecting rod and the sector plate was lower than the design requirement, increasing stress concentration, which is the main cause for the fracture of the crankshaft. In addition, bad lubrication accelerated the fracture of the crankshaft. Suggestions were made based on the study.