Matthew Perry was laid to rest this week -- and it looks like the low-key gathering featured his old costars ... who were suited and booted to honor their late, cherished comrade.

The actor's loved ones and fellow "Friends" castmates -- including Jennifer Aniston, Courteney Cox, David Schwimmer, Matt LeBlanc and Lisa Kudrow -- attended Matthew's funeral Friday at Forest Lawn Memorial Park in Los Angeles ... a famous cemetery up near the Hollywood Hills.

In fact, this place appears to have been chosen for a very specific reason ... 'cause it's just a stone's throw from the Warner Bros. Studio lot -- where they filmed their hit show.

Matthew's family carried his coffin ... with his mother, Suzanne Morrison, his father, John Bennett Perry, and his stepfather, "Dateline" correspondent Keith Morrison, among the family members in attendance.

Anyway, the ceremony looked to be relatively small ... with no more than 20 people or so standing around MP's burial plot, and some SUVs lining his gravesite. Everybody is dressed in black, of course, and it also appears some hugs and condolences are going around.

One video, in particular, shows the three ladies heading into a church ... presumably where a service was held. No clear sign of DS and MLB, but ya gotta imagine they were on hand.

Matthew's funeral comes nearly a week after his sudden passing. TMZ broke the story ... he was found unresponsive at his home last Saturday, and law enforcement believes he died by drowning -- although what exactly led up to that is still a mystery at this point.

The world at large reacted in shock to the news ... but it took a little time for the "Friends" stars themselves to speak out publicly. When they finally did, they kept their remarks brief and united --- saying they were still processing an "unfathomable loss" to their TV family.

Now, it remains to be seen if a celebration of life for fans of Perry is going to be held at some point ... but it's no surprise that this burial here was carried out on the DL.

The "Friends" crew is pretty private as it is ... and with this loss hitting as close to home as it obviously does, it makes sense that they're handling this with a lot of care/consideration.

Like we told you ... an official cause of death is undetermined at this point, pending further testing and toxicology -- not to mention an investigation by the LAPD into the exact circumstances. His body was released to his loved ones Sunday after an autopsy was done.

He was 54.