This document presents a numerical algorithm for solving second-order nonlinear fuzzy initial value problems (FIVPs). The algorithm is based on reformulating the fifth-order Runge-Kutta method with six stages (RK56) to make it suitable for solving FIVPs. RK56 is used to reduce the original nonlinear second-order FIVP into a system of coupled first-order FIVPs. The algorithm is demonstrated on a test nonlinear second-order FIVP. Results show the RK56 technique is efficient and simple to implement while satisfying fuzzy solution properties. This is the first attempt to use RK56 to solve nonlinear second-order FIVPs.