Project risk management literature commonly describes the need to rank project activities based on their risks. In the other word, the activities are ranked in base on their risks. This paper considers cost and time as two major factors for ranking projects activities base on their risks. In real world these factors are not deterministic. Thus Fuzzy theory was applied to model uncertainty. The time factor has been introduced as degree of criticality. Degree of criticality has been elicited from Fuzzy CPM model. Though, the impact of these two factors is not the same in different projects, weighted factors were applied to model this fact. At last, Fuzzy TOPSIS was used to rank project activities based on their risks.