diff --git a/Zabbix/Entities/Item.cs b/Zabbix/Entities/Item.cs
index 515fd2a..03af6c2 100644
--- a/Zabbix/Entities/Item.cs
+++ b/Zabbix/Entities/Item.cs
@@ -168,7 +168,7 @@ public class ItemPreprocessing
 
     [JsonProperty("type")] public int? Type { get; set; }
 
-    [JsonProperty("params")] public string? Params { get; set; }
+    [JsonProperty("params")] public Dictionary<string, string>? Params { get; set; }
 
     [JsonProperty("error_handler")] public int? ErrorHandler { get; set; }
 
@@ -178,7 +178,7 @@ public class ItemPreprocessing
 
     #region Constructors
 
-    public ItemPreprocessing(int type, string @params, int errorHandler, string errorHandlerParams)
+    public ItemPreprocessing(int type, Dictionary<string, string> @params, int errorHandler, string errorHandlerParams)
     {
         Type = type;
         Params = @params;
diff --git a/Zabbix/Entities/ItemPrototype.cs b/Zabbix/Entities/ItemPrototype.cs
index 610a490..dcb560b 100644
--- a/Zabbix/Entities/ItemPrototype.cs
+++ b/Zabbix/Entities/ItemPrototype.cs
@@ -73,7 +73,7 @@ public class ItemPrototype : BaseEntity
         public int? OutputFormat { get; set; }
 
         [JsonProperty("params")]
-        public string? Params { get; set; }
+        public Dictionary<string, string>? Params { get; set; }
 
         [JsonProperty("parameters")]
         public IList<object>? Parameters { get; set; }
@@ -218,7 +218,7 @@ public class ItemPrototypePreprocessing
         public int? Type { get; set; }
 
         [JsonProperty("params")]
-        public string? Params { get; set; }
+        public Dictionary<string, string>? Params { get; set; }
 
         [JsonProperty("error_handler")]
         public int? ErrorHandler { get; set; }
@@ -230,7 +230,7 @@ public class ItemPrototypePreprocessing
 
         #region Constructors
 
-        public ItemPrototypePreprocessing(int type, string @params, int errorHandler, string errorHandlerParams)
+        public ItemPrototypePreprocessing(int type, Dictionary<string, string> @params, int errorHandler, string errorHandlerParams)
         {
             Type = type;
             Params = @params;
diff --git a/Zabbix/Entities/LLDRule.cs b/Zabbix/Entities/LLDRule.cs
index ceb9fef..3d76b98 100644
--- a/Zabbix/Entities/LLDRule.cs
+++ b/Zabbix/Entities/LLDRule.cs
@@ -65,7 +65,7 @@ public class LldRule : BaseEntity
         public int? OutputFormat { get; set; }
 
         [JsonProperty("params")]
-        public string? Params { get; set; }
+        public Dictionary<string, string>? Params { get; set; }
 
         [JsonProperty("password")]
         public string? Password { get; set; }
@@ -272,7 +272,7 @@ public class LLdRulePreprocessing
         public int? Type { get; set; }
 
         [JsonProperty("params")]
-        public string? Params { get; set; }
+        public Dictionary<string, string>? Params { get; set; }
 
         [JsonProperty("error_handler")]
         public int? ErrorHandler { get; set; }
@@ -284,7 +284,7 @@ public class LLdRulePreprocessing
 
         #region Constructors
 
-        public LLdRulePreprocessing(int type, string @params, int errorHandler, string errorHandlerParams)
+        public LLdRulePreprocessing(int type, Dictionary<string, string> @params, int errorHandler, string errorHandlerParams)
         {
             Type = type;
             Params = @params;