A method for controlling starting of a Liquefied Petroleum Injection (LPI) engine of a mild hybrid electric vehicle includes driving a fuel pump when a first node of an ignition switch is selected, performing an engine cranking operation by driving a Mild Hybrid Starter & Generator (MHSG) when a second node of the ignition switch is selected, determining whether a cranking completion condition is satisfied while performing the engine cranking operation, comparing a pressure of a Liquefied Petroleum Gas (LPG) fuel with a target pressure, and controlling the MHSG to generate a torque corresponding to an idle torque of the LPI engine when the pressure of the LPG fuel is less than the target pressure.