Focusing on the distribution of accentual patterns in Sino-Japanese words, this paper mainly presents a standard Optimality-Theoretic analysis on the frequency asymmetry of Sino-Japanese words’ accents, and compares it with loanwords’ accentual patterns in Tokyo Japanese. Morphophonological constraints LexFt and MorFt separately utilized and quantity-sensitive constraint NonFin(L) newly introduced, this analysis proposes a constraint ranking that successfully generates dominant accentual patterns of both Sino-Japanese words and loanwords.