Perceived usability is an important requirement of interactive systems, affecting greatly the overall user experience. The Post-Study System Usability Questionnaire (PSSUQ) that was developed in English is a popular instrument for assessing perceived usability of interactive systems. In this paper, a first step towards standardization of a Greek version of PSSUQ, the PSSUQ-GR, is presented. To this end, the PSSUQ was translated and adapted to Greek by two HCI experts. Next, 359 participants interacted with two websites and then completed the System Usability Scale (SUS) and the PSSUQ-GR immediately after interacting with each website. Factor analysis successfully revealed a three-factor structure of the PSSUQ-GR with 12 items and item-subscales alignment close to the original PSSUQ. Reliability analysis using Cronbach’s alpha indicated that the PSSUQ-GR scale and the three subscales have a high reliability. In addition, the participants’ SUS scores and PSSUQ-GR scores were significantly and strongly correlated, which supports the validity of the PSSUQ-GR. Thus, this study found that the PSSUQ-GR (N=12 items) is a reliable and valid tool for measuring perceived usability, with a factor structure consistent with the English version of the PSSUQ.