What type of serum is it?

If it's an antioxidant serum you can use it before and wait at least 1 -2 minutes before you apply differin. but a strong strength antioxidant ( 10% and over VIT C) can mimic some of the same irritation that Differin can produce and may be hard for ur skin to sustain right away, so start off alternating and you'll know when to change it up once u build tolerance.

Night time serums often can include Glycolic acids to exfoliate.. avoid using that together with Differin ( or at all as differin will do this more effectively than AHA's) as Retinoids are rendered inactive when used directly with AHA's.. instead again alternate nights.. you will still reap the benefits of Differin.

I use Tazorac and it's a lot stronger and I use my serums ( with calming and epidermal repairing antioxidants only ie. VIt E, Green Tea, Nicinamide) before, the key is to wait in between any and all product/serum applications to allow your skin to absorb the ingredients. Otherwising u'll just waste product... ( and money cause lords knows this stuff aint cheap)

Make sure depending on your skin type, you gradually use Differin.. as if you use every night right away you could develop skin irritation/dermatitis which will make it harder for you to want to continue using it ( and u'll have to trat the dermatitis, meaning stop and start with Differin) and it takes at least 3-4 months to notice any positive changes. ( Though Differin is a lot gentler then the other retin a derivatives on the market.. specifically for those with more dry/sensitive skin)

If you find you are getting irritated/ peeling/ dry/ red ... try using a light moisturizer before the differin....dont worry your skin will still absorb the differrin but it will allow for longer use and less side effects.

And last but not least, stick to it. I've been using Tazorac 0.1% gel for the last 1yr and a half. and change my usage depending on the weather too,, only 2 night/ wk during winter cause it's soo dry and every other day or every 2 days during summer. alternating with a photostable 20% Vit C serum by PCA SKIN

If after 4-6 months your not finding much change with Differin ( This is what happened to me on the 0.3% Differin XP) then gradually ask your derm to move to the Differing XP.. and again if after 6months not enough change/positive effects or ur skin is fairly tolerable... then Tazorac ( as this is the strongest retinoid ) or Retin A, Retin A Micro if you are less acne prone etc etc. etc.

During that process you build tolerance as well for the retinoid and it will help to avoid all the icky stuff that comes along with retinoid usage for lots of people. -----

suggestion: use epidermis repairing antioxidants and moisturizers when using retinoids.. and a MUST is SPF 15 at the least .. they saved my life.. here a few of products i use(d) to help

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Cetaphil Lotion ( w/ SPF 15)
Neutrogena Ultrasheer Dry Touch SPF ( also come ins a moisturizer w/ 30 spf.. light and doesn leave a grey cast.. awesome product)
Cetaphil face wash
La Roche Posay EFFACLAR dermo-smoothing cleasing foam ( doesnt use SLS and helps to avoid stripping already sensitized skin, thus helping to repair the top layer of ur skin, plus is feeelllls awesome)
Antioxidants ( Nicinamide, present in all OLAY products and NIA 24 + VIT E my favorite one is glytone vitaceutical serum as is uses a very well researched active version of VIT E for emollient + antioxidant properties) + green tea polyphenols ( replenix serum...)
Olay Moisture balancing Face wash
Impruv face lotion
La Roche Posay Toleriane line of products

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PHEW! Lotsa stuff. hope that helps!

Ok, so apparently, retinyl palmitate is not retinol but similar to retinol.
But I am still unsure of whether it is ok to use it with differin.