Can you mix different RAM brands same sizes?

Solution
yes you can, if your motherboard supports those rams you will be able to use them without any real problems. I have 2xteam ddr 1333mhz + 1x pny ddr3 and never had any issues. The only thing I notice is that the first one is better for overclocking. But if you are not overclocking your ram, you should be fine.
yes you can, if your motherboard supports those rams you will be able to use them without any real problems. I have 2xteam ddr 1333mhz + 1x pny ddr3 and never had any issues. The only thing I notice is that the first one is better for overclocking. But if you are not overclocking your ram, you should be fine.
 
Solution
ANY time you mix DRAM it can be and often is problematic, even with the same exact model of DRAM, simply take a look through the forums, they are filled with people trying to mix DRAM (often the same exact model) and it not working. DRAM in a package has sticks that have been tested to play nice. You could go to an assembly line and pull sticks right off of it and they might well not play together.
 
While it can be problematic that's not to say it's impossible. I originally had 2 sticks of Team Vulcan memory then nearly two years later bought two more of the same model but I took care to make sure they were the same before purchase. They're currently installed, have different manufacturing dates and all 4 play nice with my memory running at 228 fsb.

I've personally never had a problem ever mixing memory with different manufacturing dates as long as they are of the same exact model....