This study aimed at finding self-regulatory capacity and habits of 3 learners with differing proficiency levels at Translation and Interpretation department of a State university in Turkey. This is a multiple case study and longitudinal in nature in which the process of vocabulary learning was observed in three subsequent school terms. The participants were chosen according to several exam grades from prep classes and out of 15 voluntary participants; three were chosen and were named as a good starter in more improving group, average starter in less improving group and a steady one in decreasing group in terms of their grades. Data collection tools included three narrations as retrospective data, six interviews and six self-reports. The collected data was analyzed according to a checklist which was modified from a scale called "Self-regulatory Capacity for Vocabulary Acquisition (SRC voc)" (Tseng et al 98). The data was coded under the subheadings of that checklist. It was concluded after the analysis that self-regulation was an important indicator and predictor for success in vocabulary acquisition. The good starter and average starter student was able to overcome some negative feelings or habits during his/her vocabulary learning process; however, the steady one was unable to create an effective balance between good and bad feelings and seemed to feel pessimistic and unsuccessful although she tried hard. Some causal attributions behind these learners' positive or negative attitudes or feelings towards vocabulary learning also seemed to play a significant role in their self-regulatory capacities in vocabulary acquisition.