This study assessed the melanogenesis effects of rice protein hydrolysate (RPH) and explored the underlying molecular mechanism of its characteristic peptides. In this investigation, human epidermal melanocyte (PIG1) cells were used to establish a UVB-induced model to evaluate the effect of RPH on melanin content, tyrosinase activity, and reactive oxygen species (ROS) levels. High performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was employed to identify the peptide composition (2–4 amino acids) in RPH. Enzymatic hydrolysis was employed to screen the characteristic peptides Leu-Leu-Lys (LLK), Leu-Pro-Lys (LPK), and pyroGlu-Lys (pEK), while their effect on the molecular mechanism involved in the melanin synthesis process was further explored using quantitative real-time polymerase chain reaction (PCR) and western blotting. The results indicated that RPH reduced the melanin content, tyrosinase activity, and ROS production in PIG1 cells. The selected peptides LLK, LPK, and pEK from RPH reduced the expression of tyrosinase-related protein 1 (TRP-1) and tyrosinase-related protein 2 (TRP-2) and affected melanin synthesis by regulating the JNK/β-Trcp/NFκB-p65/MITF signaling pathway at the mRNA and protein levels. This study shows that RPH plays a vital role in the melanogenesis process, therefore, providing a theoretical basis for the use of RPH as a novel additive product.