Assessment is a process where teacher brings in a verdict of learners'' achievement. Negotiated portfolio assessment supports learners to become members of jury and therefore, to reach their own verdict of attainment. Thus, learners, being members of jury, are encouraged to co-operate and negotiate with teacher, as well as, they are involved in making decisions about the degree to which their performance matches their ability. The study aims to investigate the influence of negotiated portfolio assessment on student motivation. Moreover, it explores the ways in which the students appeared to undergo motivation enhancement. The study also examines cases where the students experienced no motivation enhancement.