0428 GMT May 27, 2020
It is the first sanction announced by UEFA since European football's governing body said the "football family" must "wage war on the racists," BBC Sport reported.
Partial stadium closure is the minimum punishment UEFA can impose.
Lazio has been fined €20,000 (£17,300) and will suffer full stadium closure if it reoffends within a year.
The sanctions relate to incidents during Lazio's 2-1 win over French side Rennes in a Europa League group match on October 3.
That game was already subject to a partial stadium closure for the racist behavior of the Serie A side's fans in a Europa League last-32 game against Sevilla in February.
On Tuesday, UEFA defended its record of taking action against racism in the wake of England's Euro 2020 qualifier in Bulgaria.
Lazio had released a statement prior to UEFA publishing its ruling, protesting against the "deeply damaging" penalty.
The Italian club said the decision "seems not to have taken into account the clear condemnation from the club against the odious racist behavior of a few irresponsible people."
The statement added that Lazio "reaffirms its intention to pursue in penal and civil courts those responsible for unacceptable behavior".
The Italian side hosts Celtic in their next European game on November 7.