The IPCC 4th Assessment Report states that climate change, in particular increased risk of floods and droughts, is expected to have severe impact on South Asian countries, which economies rely mainly on agriculture. In fact, although South Asia has low GHG emissions, climate change has already deeply affected the economic growth and development of this region. This study examines the decadal seasonal variations in rainfall pattern calculated for summer, winter, monsoon and post-monsoon seasons and average monthly temperature is examined and their difference from (1971-1980) to (2010-2015) of selected South Asian countries (Bangladesh, India, Sri Lanka and Pakistan). The results shows that the annual rainfall variability from 1971-2015 was 15%, 17%, 20% and 12% of Bangladesh, India, Pakistan and Sri Lanka respectively. In summer season the maximum number of rainfall was take place in the decadal period of 1971-80 with (38%) variations in Bangladesh, in 1991-2000 with (285%) and (36%) variations in India and Pakistan, in 1981-90 in Sri Lanka with (30%) variations. In case of winter season, the maximum number of rainfall was taken place in 2001-2010 with (59%) variations in Bangladesh, in 2001-2010 with (170%) variations in India, in 1981-90 with (37%) variations in Pakistan and in Sri Lanka, the maximum number of variations take place in 1991-2000 with (49%) variations. The maximum rise in temperature from (1971-80) to (2010-2015) was 0.57OC in the month of May, 0.79 OC was in the month of December, was 0.95oC was in the month of October and 1.21 OC in the month of May in Bangladesh, India, Pakistan and Sri Lanka respectively. The increase in temperature, particularly the maximum temperature has been found to have considerable adverse effect on crop performances.