EN
Some relations between the James (or non-square) constant J(X) and the Jordan-von Neumann constant $C_{NJ}(X)$, and the normal structure coefficient N(X) of Banach spaces X are investigated. Relations between J(X) and J(X*) are given as an answer to a problem of Gao and Lau [16]. Connections between $C_{NJ}(X)$ and J(X) are also shown. The normal structure coefficient of a Banach space is estimated by the $C_{NJ}(X)$-constant, which implies that a Banach space with $C_{NJ}(X)$-constant less than 5/4 has the fixed point property.