Physical inactivity is a leading risk factor for global mortality with flexibility being the key factor for determining an individual's health status. This study explored the impact of physical activity on the flexibility of lumbar spine and lower extremities in undergraduates. It further explored the association between the flexibility of lumbar spine and lower limbs in individuals who shared the same amount of physical activity. The sample of 70 undergraduates was chosen from the University of Peradeniya, Sri Lanka using stratified random sampling method. 35 students from each gender were divided into three categories (low, moderate, and high) based on their physical activity level evaluated using International Physical Activity Questionnaire-short form (IPAQ-SF). Modified Schober test was used to measure the flexibility of lumbar spine while Sit-and-Reach and Groin Flexibility tests were used to measure the flexibility of lower limbs. The results showed a weak significant correlation between physical activity and flexibility of lower limbs (r=0.236, p=0.048), but no significant correlation between physical activity and flexibility of lumbar spine (r=-0.179, p=0.701). It explored a moderate positive significant correlation between the flexibility of lumbar spine and lower limbs (r= 0.536, p=0.008) in subjects who were low in physical activity but not in subjects who were moderately and highly physically active.Furthermore, the study indicated the males to be more flexible in both lumbar spine (22.3) and lower limbs (7.7) compared to the corresponding values of females (21.4 and 6.7) respectively. Therefore, it is important to take measures to alleviate the physical inactivity in young adults with low physical activity to improve the general status of health by preventing the influence of flexibility of one region on another.