Nowadays, consumer trends towards healthier and low fat products have a significant impact on the deep fat frying industry. The objective of this study was to design a modified deep fat fryer (MDF) to have a smaller surface area relative to height, with made a steam blanketing over the fryer. Different levels of water injection flow rates have been used (0.1, 0.2 and 0.3 ml/20 min. per 1 liter of tested oil), compared with conventional fryers (CDF). Frying was conducted at 170 ± 10 °C into sunflower oil using CDF (H√A = 0.24) and MDF (H√A = 0.8) in batch 8 min. 16 batches every day (eight hrs. /day)for up to 40 hrs (Consecutive five days). The modification was intended to related oil deterioration. Water injection had a dual effect. In comparison with CDF, water injection increased the acidity (expressed as oleic acid) from 0.34 % to 0.97 %, after 40 hrs at 170 ± 10 °C of deep fat frying, and a contrarily, the protective role was observed in all the other quality indices. Significant reductions in TBA values (from 8.9 to 4.81mg malonaldehyde/liter of tested oil), P-anisidine values (from 35.6 to 12.9), TPC contents (from 34.5% to 18.64%), conjugated diene (232 nm) (from 8 to 5.59) and conjugated triene (268 nm) (from 1.9 to 1.33) were recorded in sunflower oil compared with CDF. These quality indices of sunflower oil developed dramatically in the first level of water injection flow rate. Consequently, the first level of water injection had the highest (P≥0.05) inhibitory effect compared with the other levels of water injection. Fatty acid composition of fried oil properties during deep frying CDF and MDF designs were determined. There were significant differences (P≥0.05) of fatty acids composition between the fried oil induces during using of CDF and MDF designs. Total unsaturated fatty acid at MDF design gave the highest values. Also, organoleptic evaluation of fried potato chips by CDF and MDF were evaluated by panelists. Fried potato chips during the first level of water injection flow rate had the highest (P≥0.05) flavor (4), crisp (4.5), greasiness (4.6), and overall acceptability (4.8), compared with fried potato chips during other levels of water injection flow rates and with CDF. Findings suggest that determination of the oil quality indices are good makers of sensory evaluation during deep fat frying. Results indicated the changes in moisture content, oil uptake and shrinkage percentages of potato chips at different levels of water injection compared the control samples. The negative correlation coefficient between oil uptake and moisture content was high (r = -0.915) and linear regression equation for prediction the oil uptake y = 34.1064 – 2.0291X. Also, results suggest that during deep fat frying by MDF design may reduce the thermal deterioration of sunflower oil. Water injection can be applied as a simple method to improve oil quality during deep fat frying.