We analyse whether lower investments in human capital of part-time workers are due to workers' characteristics or human resource practices of the firm. We focus on investments in both formal training and informal learning. Using the dutch life-long-learning survey 2007, we find that part-time workers have different determinants for formal training and informal learning from full-time workers. The latter benefit from firms' human resource practices such as performance interviews, personal development plans, and feedback. Part-time workers can only partly compensate the lack of firm support when they have a high learning motivation and imagination of their future development