Objectives: To understand experiences with and measure the effect of mobile standing desks (MSD) on undergraduates' sedentary time (ST). Participants: Two samples of full-time undergraduates in Fall 2018. Methods: Study 1 (n = 21): baseline average daily ST was measured via activPAL4[superscript TM] inclinometers and the NIGHTLY-WEEK-U questionnaire for 7 days. Participants received a MSD for one week then intervention ST was calculated. Study 2 (n = 28): baseline ST was measured with an online NIGHTLY-WEEK-U questionnaire, participants received a MSD for one month, then intervention ST was calculated. Paired-sample t-tests assessed differences. Interviews/online questions explored experiences. Results: Study 1: objectively measured (p = 0.0045, d = 0.71) and self-report (p = 0.0005, d = 0.92) ST reduced significantly post-intervention. Study 2: ST reduced significantly post-intervention (p = < 0.0001, d = 0.98). Facilitators and barriers to desk usage were described. p d p d p d Conclusions MSD were effective for reducing undergraduates' ST across one-week and one-month.