It is known that the grain protein of ordinary maize has a low biological value due to deficiencies of balance of amino acid content. Therefore improving the limited content of amino acids like lysine, tryptophan, threonine and others is an important objective for maize breeding. The scientific works on improving the quality of maize protein began after the discovery of the biochemical effect of the recessive gene opaque-2 (o2), which transformed a horny endosperm in floury texture of the endosperm and changed the synthesis of protein fractions. In consequence of the redistribution of protein fractions’ conditions, considerably reduces the zein content and increases the content of albumins, globulins and glutamines of fractions rich in lysine, tryptophan and other essential amino acids. The opaque-2 maize with high content of lysine guarantees the nutritive value of grain used in food of people and forage of animals. In this paper, we presented the progress of our breeding research in order to improve quality of maize. As a result of our work during long time (1076-2014 years), numerous forms of inbred lines and hybrids of o2 maize were created. The initial material of working collection consists of more than 550 inbred lines with grain o2 and mo2, gene recombination as o2su2, o2wx1, lines higher in protein and higher in oil. Their matching has a high combining ability for productivity, resistance to diseases of plant, ear and grain, tolerance to drought and high temperature etc. More than 70 inbred lines with high quality of grain ware included in World Collection of Plant Genetic Resources of All-Russian Research Institute of Plant Genetic Resources N. I. Vavilov from Saint Petersburg city and Centre of Genetic Vegetable Sources of the Scientific Research Institutes of ISC of the Republic of Moldova too.  After application of the new lines in crossing, a lot of hybrids of opaque-2 maize were created and evaluated, including those with high content of protein, oil and modified grain.  Recently, two competitive o2 hybrids were regionalized: Chisinau 307 PL and Chisinau 401 L mo2. The Chisinau 307PL manifested a high content of protein (12.0-12.5%) and lysine (4.12-4.50%) in grain and yield – till 14.9 t/ha. The Chisinau 401 L mo2 has a modified structure of endosperm grain, protein content about 10.8% and 3.98-4.00% – of lysine, and kernel yield – till 15.9 t/ha. The lysine production of these hybrids is 34 kg/ha and 30 kg/ha, respectively. The nutritive value of grain of hybrid Chisinau 307 PL used as fodder for pigs, showed a higher nutritious capacity with 49.5% more in comparison with normal maize. The hybrids may be cultivated up to 50-55 thousands plants per ha in all agrarian farms of our country. At the time, we can submit to the State Commission for Plant Variety Testing, two new hybrids with high productivity and quality of grain.  The hybrids of maize with high quality of grain represent important raw material for fodder, contribute to reducing the protein malnutrition of humans, the cost of feed supplement for monogastric animals and promote the improvement of economical efficiency of agricultural branches.