Pathfinder is a widely applied method for structural knowledge assessment. Concept mapping is a theory-based strategy of instruction and evaluation. In this study, we combined the ´knowledge elicitation´ and ´knowledge representation´ procedures of concept mapping, the knowledge-structure evaluation algorithms of Pathfinder, and the scoring rubrics of concept mapping proposed by Novak & Gowin (1984)to implement two indices for assessing structural knowledge--the concept mapping based closeness index (CMC) and the Novak-Gowin index(N-G).To explore the predictive and discriminant validities of CMC,N-G, the PFC and PRX indices obtained from Pathfinder, and the possible redundancy among them,153 college students´ concept maps and similarity judgement data of 31 concepts from the ´learning theories´, and their achievement scores of educational psychology, were collected. The results showed: 1. All the four indices were significantly correlated to the achievement score of educational psychology. The PFC, PRX, CMC, and N-G accounted for 36%, 16%, 36%, and 23% of the variances of the achievement score, respectively. 2. The results of discriminant analysis showed that the PFC, CMC, and N-G indices correctly discriminated 80% of the group memberships of the students of the high- or low achievement groups. Yet the PRX was excluded from the discriminant function. 3. The PFC, CMC, and N-G indices, though elicited and computed through different procedures, correlated significantly with each other. The result of partial correlation showed that when the influence of any index was controlled, the other indices were still correlated significantly with the achievement score. Therefore, though there might be redundant components among those indices, they did remain their own unique components.