Field experiments were conducted at Tamil Nadu Agricultural University. Coimbatore from 1994, covering two kharif and two summer seasons, to evaluate the influence of seasons on the yield of soybean. The yield increase in soybean during summer season was 8.7 per cent over kharif season. The agro-meteorological parameters computed indicated that Growing Degree Days (GDD) and Photothermal Unit (PTU) were comparatively higher for kharif seasons than summer season. However. Heliothermal. Unit (ITU) and Heat Unit Efficiency (HUE) were higher for summer (1995 and 1996) as compared to the Kharif.