Blood pressure in our body is finely regulated through autonomic nervous system and cardiac centers and studies established that parasympathetic dominance exerted by slow deep breathing decreases blood pressure. Reaction time is an estimate of the subject's capacity for inhibiting pre-potent motor responses. Decreased reaction time indicates greater alertness, faster information processing and less distractibility. Nevertheless, there has been conflicting results about the effect of deep slow breathing on reaction time The present research targeted a community based cross sectional observational study (n=80, age=17-70 years) performed in Lalitpur Municipality, Ward number-14, Nepal from May 2019 to June 2019, to observe the immediate effect of slow deep breathing exercise on blood pressure and reaction time by using online visual reaction time test. Volunteers performed the slow breathing exercise (approximately 4seconds inhalation and 6 seconds exhalation) in Sukhasana for 5 minutes. Base-line and post-slow-breathing blood pressure and visual reaction time was recorded and compared. Decrease in systolic and diastolic pressure was recorded in all, but statistically insignificant. Among the whole study population, significant decrease (p<0.001) in reaction time was noted (90.35±13.96 msVs 76.68±9.90 ms). Among male subjects of age-group 17-28 years, and 50-70 years, significant decrease in reaction time was noted (p<0.05) whereas, among the female subjects of all age groups, reaction time decreased significantly (p<0.05). Decrease in reaction time signifies improved central neuronal processing activity. This may be due to greater arousal, faster information processing, and ability to ignore or inhibit extraneous stimuli. Hence, regular practice of slow deep breathing exercise may be beneficial to lower blood pressure and to improve concentration.