A field experiment was performed to recommend suitable fertilization formula in Virginia tobacco farmers fields in Mazandaran in two years (1998-1999). According to the soil analysis and amount of available K (ppm), 9 farms were selected and divided to three equal groups (<200, 201-300 and >300 ppm available K). In each farm, the experimental design was RCBD with four treatments (0, 100, 150 and 200 kg K₂O/ha) and three replications. The results showed that in the first group (less than 200 ppm) there were no significant difference between treatments in three farms for yield, value, leaf potassium, nicotine, sugar and ash factors. But the results of combined analysis of variance on farms in the first group showed that the difference in value was significant at 5% threshold and there was an increase in yield as K rates increased. In the second group (201-300 ppm) the difference in yield was significant at 5% threshold on one farm, but there were no significant difference on two other farms for yield, value, leaf potassium, nicotine, sugar and ash factors. The results of combined analysis of variance for the second group showed that there was a significant difference in yield at 5% threshold. In the third group (more than 300 ppm), there were no significant difference between treatments. But the results of combined analysis of variance for the third group showed that there was a significant difference for yield at 5% threshold. In general the results showed that potassium available critical level, Cate-Nelson, Mitcherlich-Bray equation and economic critical level were 264, 247 and 258 ppm respectively.