A field experiment was conducted at the experimental farm of Bangladesh Institute of Nuclear Agriculture, Mymensingh during October 2007 to March 2008 to investigate the morpho-physiological characters, yield attributes and yield of ten exotic and two local onion genotypes viz. AV-15142, AV-17070, AV-21844, AV-21848, J-315, J-368, J-420, JM-315, JM-368, JM-420, BARI Piyaj-2 and BARI Piyaj-3. Among the genotypes BARI Piyaj-2 and BARI Piyaj-3 were the recommended varieties for both winter and summer cultivation and the rest of the genotypes were exotic. The experiment was laid out in a Randomized Complete Block Design with three replications. Significant variations were found in all the morpho-physiological and yield contributing characters of onion. Results revealed that higher yield performing genotypes produced taller plants, higher number of leaves plant-1, longer and thicker leaves and thicker pseudostem except J-420. The exotic line J-420 showed superiority in plant height, leaf number, leaf length, leaf breadth and pseudostem diameter with intermediate yield. Investigation showed that low yield performing genotypes produced shorter plants, lower number of leaves and shorter leaves which resulted in lower bulb yield. Similarly, high yield performing genotypes produced thicker and larger bulb which resulted in higher bulb yield. The bulb of JM-315 matured earlier but showed lower performance in bulb yield. The genotypes AV-21844 and AV-21848 showed superiority in yield contributing characters. The genotype AV-21844 showed best performance in respect to storage quality, unsplitted bulb production, days to maturity of the bulb and bulb yield.