Chlorella vulgaris was isolated from the Nile River, Qalubia Governorate, Egypt, for possible use in biodiesel production. BG-II nutrient growth media was used for isolation and laboratory growth. Identification was performed via 18S rRNA gene amplification followed by sequencing. Alga was exposed to UV-C (254 nm) for three different times aiming at the improving of dry weight accumulation as well as increasing oil production. Three different times of exposure to UV-C were applied i.e.; 15, 30, and 45 sec. Daily measurement of dry weight (g·l-1) was performed. Oil content and volumetric lipid productivity (Lp) were also determined. UV-C exposure led to increasing volumetric lipid productivity by 27, 27.3, and 32.4 mg·l-1·d-1 with 15, 30 and 45 sec; respectively as compared with the control one which resulted in 18 mg·l-1·d-1. Of the examined mutants, the highest one in concern productivity was re-irradiated by four exposure times of UV-C (254 nm) for 15, 30, 45 and 60 sec. At 15 sec, the oil content was raised to be 34%; while 31% was obtained at 30 sec and downed to be 22% at 45 and 60 sec of exposure time. Fatty acid methyl ester profile was 82.22% in the first mutant at 45 sec compared with the wild strain that contains total of 66.01% of FAs. Furthermore, the highest levels of polyunsaturated fatty acid methyl ester (PUSFAs) were observed in the mutant exposed at 45 sec of first exposure and reached 11.41% which in turn reduced the cetane number to 71.3.