Microwave expansion of imitation cheese is a novel way of producing a potentially health crispy snack food. This study aimed to investigate the effects of protein:starch (P:S) ratios of 37:0, 24:13, 20:17 or 16:21 and refrigerated storage (1–9 days) on the functional properties, water mobility and microwave expansion of imitation cheese. Cheese hardness and rheological dynamic moduli decreased while water mobility increased with decreasing P:S ratio and prolonged storage time. The volumetric expansion increased with increasing storage time pre-microwaving. After storing cheeses for 9 days, a cheese with P:S of 37:0 and protein:emulsifying salt ratio of 17.12 exhibited the highest expansion of ∼1050%, while cheese with P:S of 20:17 exhibited the highest volumetric expansion of ∼900% among cheeses containing starch. The expansion of cheese with P:S of 37:0 suggests strongly that it is mainly the hydrated protein matrix that stretches under pressure generated by steam during microwaving to form the expanded structure.