Subjective life expectancy (SLE) has been related to psychological variables, such as optimism. Based on previous studies where positive attitude was related with longer lifetime, the present study examined whether modifying participants’ attitude would influence their SLE. Therefore, 50 participants were randomly assigned either to a positive or to a neutral attitude group. During one week, participants of the positive (neutral) group, had to choose the three most accurate positive (neutral) sentences (among 22) to describe their day. After this week, they had to estimate the probability of being 60, 70, 80, or 90 years old (traditional measure) and to situate themselves on a line representing their lifetime (spatial based measure). Results show that 1) a more positive attitude increased SLE more than a neutral one, 2) the spatial based measure was sensitive to the intervention and 3) both measures correlated positively with participants’ optimism.