With a growing world population, resource use, and the effects of climate change, it is apparent that our current ‘take-make-dispose’ economy cannot be sustained. Sustainable business model innovation integrates sustainability objectives into business models to achieve a positive impact on society and/or the environment in combination with pursuing profit. Experimentation capabilities are essential for implementation, but established companies struggle with execution. Start-ups are more acquainted with a trial and error approach in which assumptions are gradually validated or adapted to market needs. To contribute to the shift towards sustainable business models, this paper explores how start-ups develop sustainable business model experiments and which elements of the sustainable business model canvas are tested through experimentation. Three start-ups were followed in their experimentation journey to develop profitable sustainable business models. Results indicate that 1) experiments always concerned the value proposition and another building block of the business model with a high-risk profile 2) start-ups use easy accessible resources to execute experiments in a fast paced and iterative manner 3) decisions of continuation of business model ideas were based on the outcomes of experiments in relation to the purpose of the company. In addition, this paper provides examples of experimentation practices of these start-ups to give hands-on examples how sustainable business model experimentation can be developed.