Dendrobium officinale has attracted increasing attention as a functional food because of its diverse biological activities; however, the photoprotective potential of its protein-derived peptides remains poorly understood. In this study, D. officinale protein hydrolysates were fractionated by ultrafiltration according to molecular weight, and their protective effects against ultraviolet B (UVB)-induced photoaging were systematically evaluated in HaCaT keratinocytes. Among the tested fractions, low-molecular-weight peptide fractions exhibited relatively stronger antioxidant activity and effectively reduced intracellular reactive oxygen species (ROS) accumulation in UVB-irradiated cells. In addition, the peptide fractions alleviated UVB-induced inflammatory responses and decreased matrix metalloproteinase (MMP) expression, which was associated with modulation of mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways. Higher-molecular-weight fractions showed relatively stronger effects on maintaining skin barrier-related functions and were associated with regulation of transforming growth factor-β/Smad (TGF-β/Smad) signaling and collagen-related protein expression. Overall, these findings demonstrate functional differences among Dendrobium officinale peptide fractions and suggest their potential application as natural photoprotective ingredients in functional foods and cosmeceutical products.