Pulmonary artery hypertension (PAH) is a rare, progressive, and fatal cardiovascular disease. Several epidemiological PAH registries showed that the most common age of PAH patients is between 41-50 years (mean age of 46.8 years). However, the reason why PAH is more susceptible for young remains unclear. In the present study, the survival rate and morphological changes of monocrotaline (MCT)-induced pulmonary hypertensive (PH) rats were compared between young (4-week-old) and adult (17-week-old). The Kaplan-Meier survival analysis revealed that young sham-treated rats were survived at day 35, whereas young MCT-PH rats were died at mean 22.4 days after MCT injection. Interestedly, adult MCT-PH rats were survived over 42 days, similar to adult sham-treated rats. The weights of heart and pulmonary artery were increased in young MCT-PH rats. Similar increases were also observed in adult MCT-PH rats. In addition, the expression level of Ca²⁺-sensing receptor (CaSR) and transient receptor potential canonical channel 6 (TRPC6), which were identified as molecules associated with the pathogenesis of PAH, were compared between young and adult MCT-PH rats. Their expressions were upregulated in both groups. Further analyses are necessary for elucidating the mechanism underlying the age difference in PAH patients.