In this paper, we propose a strategy to improve scalability of replicatedservices in mobile agent systems by using an appropriate passive replication protocol for each replicatedservice according to whether the service is deterministic or non-deterministic. For this purpose, two passive replication protocols are introduced for nondeterministic and deterministic services respectively. They both allow visiting mobile agents to be forwardedto andexecute their tasks on any node performing a service agent, not necessarily the primary agent. Additionally, in the second protocol for deterministic services, after a backup service agent has receivedeac h mobile agent request andobtainedits delivery sequence number from the primary service agent, the backup is responsible for processing the request andco ordinating with the other replica service agents. Therefore, our strategy using the two proposedproto cols can promise better scalability of replicatedservices a large number of mobile agents attempt to access in mobile agent systems.