diff --git a/src/google/adk/evaluation/evaluation_generator.py b/src/google/adk/evaluation/evaluation_generator.py
index 1d9662bdc2..b6e24b44f2 100644
--- a/src/google/adk/evaluation/evaluation_generator.py
+++ b/src/google/adk/evaluation/evaluation_generator.py
@@ -356,7 +356,7 @@ def _get_app_details_by_invocation_id(
           agent_name = event.author
           app_details.agent_details[agent_name] = AgentDetails(
               name=agent_name,
-              instructions=llm_request.config.system_instruction,
+              instructions="\n\n".join(llm_request.config.system_instruction) if isinstance(llm_request.config.system_instruction, list) else llm_request.config.system_instruction or "",
               tool_declarations=llm_request.config.tools or [],
           )