Background Depression has a high impact on both patients and the people around them. These non-professional caregivers often experience overburdening and are at risk for developing psychological symptoms themselves. Internet interventions have the potential to be accessible and (cost)-effective in terms of reducing and preventing psychological symptoms. Less is known about their potential to decrease psychological distress among caregivers. The primary aim of this study is to evaluate (1) the user-friendliness and (2) the initial short-term effects on psychological distress of ‘E-care for caregivers’, an internet based guided self-management intervention for non-professional caregivers of depressed patients. Methods A pilot randomized controlled trial (RCT: n = 80) comparing ‘E-care for caregivers’ (n = 41) with a waitlist-control group (n = 39). The primary outcome measure (user-friendliness) was assessed with the System Usability Scale (SUS) and semi-structured telephone interviews among participants. Interviews were qualitatively analyzed with thematic content analysis. Secondary outcomes were assessed through online questionnaires administered at baseline and post-intervention at six weeks among caregivers. Statistical analyses were conducted according to the intention-to-treat principle using regression techniques for the secondary outcomes. Results All participants were recruited within six weeks through online advertising. Two-thirds of participants experienced higher levels of psychological distress (K10 > 20). The internet intervention was evaluated as user-friendly by caregivers (average score of 81.5, range [0–100]). Results did not show a reduction in psychological distress or other secondary outcome measures. Sensitivity analyses showed a decreased quality of life in the control condition compared to the intervention condition (p = 0.02, Cohen's d = 0.44) and higher levels of mastery (p = 0.02, Cohen's d = 0.48) in the intervention condition compared to controls. Discussion The internet intervention was evaluated positively for usability and was considered as easy to use. The study did not show a reduction in symptoms of psychological distress. However, there were some indications that those completing the internet intervention perceived higher levels of mastery and a protective effect in quality of life post-intervention. Strengths and limitations As far as we know, this study is the first to examine the user-friendliness and initial effects of an internet intervention specifically designed for non-professional caregivers of depressed patients. As this was a pilot study, the findings should be interpreted with caution. We recommend investigating the possibilities of providing a (partially) sequential design as well as incorporating themes like stigma and expressed emotion in the online course and subsequent evaluation of the internet intervention in a full-scale RCT, with a six-month follow-up. Trial registration Netherlands Trial Register: NTR5268. Registered on 30 June 2015.