The classification performance of nearest prototype classifiers largely relies on the prototype learning algorithms, such as the learning vector quantization (LVQ) and the minimum classification error (MCE). This paper proposes a new prototype learning algorithm based on the minimization of a conditional log-likelihood loss (CLL), called log-likelihood of margin (LOGM). A regularization term is added to avoid over-fitting in training. The CLL loss in LOGM is a convex function of margin, and so, gives better convergence than the MCE algorithm. Our empirical study on a large suite of benchmark datasets demonstrates that the proposed algorithm yields higher accuracies than the MCE, the generalized LVQ (GLVQ), and the soft nearest prototype classifier (SNPC).