A hydraulic pressure supply system of an automatic transmission for a vehicle which generates low hydraulic pressure and high hydraulic pressure using oil stored in an oil pan and supplies the low hydraulic pressure and the high hydraulic pressure respectively to a low pressure portion and a high pressure portion. The system includes a low-pressure hydraulic pump driven by a first power source so as to pump the oil stored in the oil pan, generating the low hydraulic pressure, and supplying the low hydraulic pressure to the low pressure portion, and a high-pressure hydraulic pump driven by a second power source and fluid-connected to the low-pressure hydraulic pump so as to receive the low hydraulic pressure from the low-pressure hydraulic pump, changing the low hydraulic pressure into the high hydraulic pressure, and supplying the high hydraulic pressure to the high pressure portion.