Two novel rearranged abietane-type diterpene acids, karamatsuic acid (1) and larikaempferic acid (2) were isolated as their corresponding methyl esters, 1a and 2a, from the leaves of Larix kaempferi (Lamb.) Carr. Their structures were established as 9,10 alpha-epoxy-9,10-seco-abieta-8,11,13-trien-18-oic acid and 9 alpha,13 alpha-epoxy-8-oxo-9(8-->7)abeo-7 beta H-abietan-18-oic acid, respectively, by spectral evidence. Compounds 1a, 2a and 12,15-dihydroxydehydroabietic acid (3) exhibited potent inhibitory effects against 12-O-tetradecanoylphorbol 13-acetate (TPA)-induced Epstein-Barr virus early antigen (EBV-EA) activation in Raji cells.