Bacterial distribution analysis of the atmospheric air of fourteen primary and sixteen secondary school classes at Ibb City in Yemen was performed during the period between February and May, ٢٠٠٢. The results indicated that bacteria grown on the blood agar formed the highest numbers, followed those grown on nutrient agar, and finally on MacConkey agar. The average number of blood agar grown bacteria in nonventilated, semi-ventilated, and well--ventilated school classes were ٤٩٢, ٢٦٩, and ٢٤٦ cfu/٥٠ liters of air sample respectively. Primary schools showed a higher values of bacterial counts, compared to the secondary schools. The concentration of the bacteria inside the school classes was higher than those of school square. Inside the classes, in spite of approximate values of student per unit area, i.e. ٠,٦٤m٢, the total number of bacteria per cubic meter was observed to be inversely proportional with the class volume.