This article describes the findings of a study on the correlations between English as second language (ESL) motivation, understood as a product of the stimulus appraisal system, and writing proficiency in English among undergraduate Indian ESL learners. The principal objective of the study was to analyze the correlation between the undergraduate Indian ESL learner's motivational sub-checks/constructs, constituted using the stimulus appraisal (SA) theory of affect, and their writing proficiency in English. Additionally, it also attempted to understand the influence of sex and academic disciplines on the correlations. An ESL motivation survey was conducted using a modified version of the Attitude and Motivation Test Battery (Gardner, 1985) on students (N>350) studying in undergraduate programs in the academic disciplines of engineering, humanities, and medical sciences selected using criterion-based sampling, followed by a writing proficiency test in English. It was observed that need/compatibility factors did not significantly correlate with ESL writing proficiency in any of the three subsamples. ESL classroom-related factors within the pleasantness/novelty construct, on the other hand, significantly correlated with ESL writing proficiency. It is hoped that the insights obtained in the study should potentially help design more empirically informed pedagogical methods of ESL teaching.