: In this paper, we propose two procedures for multiplication and division using DNA strands. We first show a procedure for multiplication of a pair of two binary numbers. The procedure executes multiplication for two binary numbers of m bits in O(log m) steps using O(m2 ) DNA strands. The procedure mainly consists of bit-shift and addition operations. We next show a procedure for division of a pair of two binary numbers. The procedure executes division for two binary numbers of m bits in O(log m) steps using O(m2 ) DNA strands. The procedure first computes a reciprocal of a number using Newton's method, and then, computes a quotient of the division using multiplication and subtraction. The procedure also computes a remainder of the division using multiplication and subtraction.